Light-emitting device and manufacturing method thereof

ABSTRACT

An object of the invention is to improve the reliability of a light-emitting device. Another object of the invention is to provide flexibility to a light-emitting device having a thin film transistor using an oxide semiconductor film. A light-emitting device has, over one flexible substrate, a driving circuit portion including a thin film transistor for a driving circuit and a pixel portion including a thin film transistor for a pixel. The thin film transistor for a driving circuit and the thin film transistor for a pixel are inverted staggered thin film transistors including an oxide semiconductor layer which is in contact with a part of an oxide insulating layer.

TECHNICAL FIELD

The present invention relates to a light-emitting device including alayer containing an organic compound as a light-emitting layer, and amanufacturing method for the light-emitting device. For example, thepresent invention relates to an electronic device in which alight-emitting display device having an organic light-emitting elementis mounted as a component.

Note that in this specification, a semiconductor device refers to alldevices that can function by utilizing semiconductor characteristics,and electro-optic devices such as light-emitting devices, semiconductorcircuits, and electronic devices are all semiconductor devices.

BACKGROUND ART

A light-emitting element using an organic compound as a light-emittingbody, which has features such as thinness, lightness, high-speedresponse, and DC drive at a low voltage, has been examined to be appliedto a next-generation flat panel display or next-generation lighting. Inparticular, a display device in which light-emitting elements arearranged in matrix is considered to have advantages in a wide viewingangle and excellent visibility over a conventional liquid crystaldisplay device.

A light-emitting mechanism of a light-emitting element is thought asfollows: when voltage is applied between a pair of electrodes with an ELlayer interposed therebetween, electrons injected from a cathode andholes injected from an anode are recombined at emission centers in theEL layer to form molecular excitons, and the molecular excitons releaseenergy and emit light when relax to the ground state. Singlet excitationand triplet excitation are known as excited states, and it is consideredthat light emission can probably be achieved through either of theexcited states.

An EL layer included in a light-emitting element has at least alight-emitting layer. In addition, the EL layer can have a stacked-layerstructure including a hole-injection layer, a hole-transport layer, anelectron-transport layer, an electron-injection layer, or the like, inaddition to the light-emitting layer.

Further, as a material having semiconductor characteristics, metaloxides attracts attention. Examples of such metal oxides havingsemiconductor characteristics include tungsten oxide, tin oxide, indiumoxide, zinc oxide, and the like. Thin film transistors in which achannel formation region is formed of such metal oxides havingsemiconductor characteristics are already known (Patent Documents 1 and2).

Furthermore, a TFT including an oxide semiconductor has highfield-effect mobility. Thus, the TFT can be used to form a drivingcircuit of a display device or the like.

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2007-123861-   [Patent Document 2] Japanese Published Patent Application No.    2007-096055

DISCLOSURE OF INVENTION

For a thin film transistor using an oxide semiconductor film, high speedoperation, a comparatively easy manufacturing process, and sufficientreliability are required.

One object of the present invention is to improve operationcharacteristics and reliability of a thin film transistor using an oxidesemiconductor film.

In particular, a thin film transistor used for a driving circuit portionpreferably operates at high speed.

For example, the operation speed becomes higher when the channel length(L) of a thin film transistor is shortened or when the channel width (W)is increased. However, in the case where the channel length (L) isshortened, there is a problem of switching characteristics, for example,an on/off ratio becomes small. In addition, when the channel width (W)is increased, there is a problem in that the capacity load of a thinfilm transistor itself is increased.

Therefore, an object of the present invention is also to provide alight-emitting device including a thin film transistor having stableelectric characteristics even when the channel length is short.

In addition, when a plurality of circuits which are different from eachother is formed over an insulating surface, for example, when a pixelportion and a driving circuit portion are formed over one substrate,excellent switching characteristics such as a high on/off ratio areneeded for a thin film transistor used for the pixel portion, while highoperation speed is needed for a thin film transistor used for thedriving circuit portion. In particular, a thin film transistor used fora driving circuit portion preferably operates at high speed, sincewriting time of a display image is reduced as a resolution of a displaydevice is increased.

Another object of the present invention is to reduce variations inelectric characteristics of a thin film transistor using an oxidesemiconductor film.

Still another object of the present invention is to give flexibility toa light-emitting device having a thin film transistor using an oxidesemiconductor film.

A thin film transistor including a light-emitting element and an oxidesemiconductor layer is formed over a flexible substrate, and a flexiblelight-emitting device is manufactured.

A thin film transistor including a light-emitting element and an oxidesemiconductor layer may be directly formed over a flexible substrate.Alternatively, a thin film transistor including a light-emitting elementand an oxide semiconductor layer may be formed over a manufacturingsubstrate, and after that, the thin film transistor may be separated andtransferred to a flexible substrate. Note that in order to separate andtransfer a thin film transistor from a manufacturing substrate to aflexible substrate, a separation layer is provided between themanufacturing substrate and the thin film transistor including alight-emitting element and an oxide semiconductor layer.

For a flexible substrate, for example, a polyester resin such aspolyethylene terephthalate (PET) or polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, or a polyvinylchloride resin can be preferably used. Astructure body in which a fibrous body is impregnated with an organicresin (so-called prepreg) may also be used as a flexible substrate.

In addition, a metal substrate which is made thin enough to haveflexibility may be used. The metal substrate is provided on the sidethrough which light is not extracted. A material for forming the metalsubstrate is not limited to a particular material, but aluminum, copper,nickel, an alloy of metal such as an aluminum alloy or stainless steel,or the like can be preferably used.

One embodiment of the present invention is a light-emitting deviceincluding: a driving circuit portion having a thin film transistor for adriving circuit; and a pixel portion having a thin film transistor for apixel, which are formed over one flexible substrate. The thin filmtransistor for a driving circuit and the thin film transistor for apixel each include: a gate electrode layer, a gate insulating layer overthe gate electrode layer, an oxide semiconductor layer over the gateinsulating layer, a source electrode layer and a drain electrode layerover the oxide semiconductor layer, and an oxide insulating layer overthe oxide semiconductor layer, the source electrode layer, and the drainelectrode layer, which is in contact with a part of the oxidesemiconductor layer. In the pixel portion, a color filter layer isprovided over the oxide insulating layer, and a stack of a firstelectrode layer, an EL layer, and a second electrode layer, which iselectrically connected to the thin film transistor for a pixel, isprovided over the color filter layer. In the thin film transistor for adriving circuit, a conductive layer overlapping with the gate electrodelayer and the oxide semiconductor layer is provided over the oxideinsulating layer. The gate electrode layer, the source electrode layer,and the drain electrode layer are each a metal conductive film.

Another embodiment of the present invention is a light-emitting deviceincluding: a driving circuit portion having a thin film transistor for adriving circuit; and a pixel portion having a thin film transistor for apixel, which are formed over one flexible substrate. The thin filmtransistor for a driving circuit and the thin film transistor for apixel each include: a gate electrode layer, a gate insulating layer overthe gate electrode layer, an oxide semiconductor layer over the gateinsulating layer, a source electrode layer and a drain electrode layerover the oxide semiconductor layer, and an oxide insulating layer overthe oxide semiconductor layer, the source electrode layer, and the drainelectrode layer, which is in contact with a part of the oxidesemiconductor layer. In the pixel portion, a color filter layer isprovided over the oxide insulating layer, and a stack of a firstelectrode layer, an EL layer, and a second electrode layer, which iselectrically connected to the thin film transistor for a pixel through aconnection electrode layer, is provided over the color filter layer. Inthe thin film transistor for a driving circuit, a conductive layeroverlapping with the gate electrode layer and the oxide semiconductorlayer is provided over the oxide insulating layer. The gate electrodelayer, the source electrode layer, and the drain electrode layer areeach a metal conductive film.

As the thin film transistor for a pixel and the thin film transistor fora driving circuit, an inverted staggered thin film transistor with abottom-gate structure is used. The thin film transistor for a pixel andthe thin film transistor for a driving circuit are each a channel-etchedthin film transistor in which the oxide insulating film is provided incontact with the oxide semiconductor layer exposed between the sourceelectrode layer and the drain electrode layer.

The thin film transistor for a driving circuit has a structure in whichthe oxide semiconductor layer is sandwiched between the gate electrodeand the conductive layer. With this structure, variation in thresholdvoltage of the thin film transistor can be reduced; accordingly, alight-emitting device including the thin film transistor with stableelectric characteristics can be provided. The conductive layer may havethe same potential as the gate electrode layer or may have a floatingpotential or a fixed potential such as GND potential or 0 V. By settingthe potential of the conductive layer to an appropriate value, thethreshold voltage of the thin film transistor can be controlled.

The thin film transistor for a pixel and a pixel electrode may be formedin direct contact with each other or may be electrically connectedthrough the connection electrode layer. As the connection electrodelayer, a film including an element selected from Al, Cr, Cu, Ta, Ti, Mo,and W as its main component or a stacked-layer film including the filmand an alloy film of any of the elements can be used.

The conductive layer formed over the oxide semiconductor layer of thethin film transistor for a driving circuit, a first wiring (alsoreferred to as a terminal or a connecting electrode), and a secondwiring (also referred to as a terminal or a connecting electrode) may beformed in the same process as the pixel electrode using indium oxide, anindium oxide-tin oxide alloy, an indium oxide-zinc oxide alloy, or oxideconductive materials such as zinc oxide, or in the same process as theconnecting electrode layer using a method material such as a filmincluding an element selected from Al, Cr, Cu, Ta, Ti, Mo, and W as itsmain component or an alloy film of any of the elements.

In addition, light-emitting elements emitting light of a plurality ofemission colors, and thin film transistors for pixels which areelectrically connected to the light-emitting elements, may be formedover one substrate, so that a light-emitting device such as a displaydevice can be manufactured.

Further, a plurality of light-emitting elements emitting white light maybe provided and an optical film, specifically color filters may beprovided so as to overlap with light-emitting regions of thelight-emitting elements, whereby a light-emitting display device capableof full-color display can be manufactured. Note that in thisspecification, the color filter refers not to a whole film includingcolor filter layers with three colors (e.g., a red color filter, a bluecolor filter, and a green color filter) in addition to a black matrix oran overcoat, but to a color filter with one color.

One embodiment of the present invention to realize the above structureis a method for manufacturing a light-emitting device including thesteps of: forming a gate electrode layer using a metal conductive filmover a flexible substrate having an insulating surface and including adriving circuit portion and a pixel portion; forming a gate insulatinglayer over the gate electrode; forming an oxide semiconductor layer overthe gate insulating layer; forming a source electrode layer and a drainelectrode layer using a metal conductive film, over the oxidesemiconductor layer which is dehydrated or dehydrogenated and is notexposed to air so as to prevent water or hydrogen from entering again;forming an oxide insulating layer over the oxide semiconductor layer,the source electrode layer, and the drain electrode layer, which is incontact with a part of the oxide semiconductor layer, thereby forming athin film transistor for a driving circuit over the driving circuitportion, and forming a thin film transistor for a pixel over the pixelportion; in the pixel portion, forming a color filter layer over theoxide insulating layer, forming a first electrode layer over the colorfilter layer, which is electrically connected to the thin filmtransistor for a pixel, forming an EL layer over the first electrodelayer, and forming a second electrode layer over the EL layer; and inthe driving circuit portion, forming a conductive layer, in the sameprocess as the first electrode layer, over the oxide insulating layeroverlapping with the gate electrode layer and the oxide semiconductorlayer of the thin film transistor for a driving circuit.

Another embodiment of the present invention to realize the abovestructure is a method for manufacturing a light-emitting deviceincluding the steps of: forming a gate electrode layer over a flexiblesubstrate having an insulating surface and including a driving circuitportion and a pixel portion; forming a gate insulating layer over thegate electrode using a metal conductive film; forming an oxidesemiconductor layer over the gate insulating layer; forming a sourceelectrode layer and a drain electrode layer using a metal conductivefilm, over the oxide semiconductor layer which is dehydrated ordehydrogenated and is not exposed to air so as to prevent water orhydrogen from entering again; forming an oxide insulating layer over theoxide semiconductor layer, the source electrode layer and the drainelectrode layer, which is in contact with a part of the oxidesemiconductor layer, thereby forming a thin film transistor for adriving circuit over the driving circuit portion, and forming a thinfilm transistor for a pixel over the pixel portion; in the pixelportion, forming a color filter layer over the oxide insulating layer,forming a first electrode layer over the color filter layer, which iselectrically connected to the thin film transistor for a pixel through aconnection electrode layer; forming an EL layer over the first electrodelayer, and forming a second electrode layer over the EL layer in thedriving circuit portion, and forming a conductive layer in the sameprocess as the connection electrode layer, over the oxide insulatinglayer overlapping with the gate electrode layer and the oxidesemiconductor layer of the thin film transistor for a driving circuit.

Another embodiment of the present invention to realize the abovestructure is a method for manufacturing a light-emitting deviceincluding the steps of: forming a separation layer over a manufacturingsubstrate having an insulating surface and including a driving circuitportion and a pixel portion; in the driving circuit portion, forming athin film transistor for a driving circuit having an oxide semiconductorlayer over the separation layer; in the pixel portion, forming a thinfilm transistor for a pixel having an oxide semiconductor layer over theseparation layer and forming a first electrode layer electricallyconnecting to the thin film transistor for a pixel; transferring thethin film transistor for a driving circuit, the thin film transistor fora pixel, and the first electrode layer from the manufacturing substrateto a supporting substrate using the separation layer; transferring to aflexible substrate the thin film transistor for a driving circuit, thethin film transistor for a pixel, and the first electrode layer whichhave been transferred to the supporting substrate forming an EL layerover the first electrode layer which has been transferred to theflexible substrate; and forming a second electrode layer over the ELlayer.

Another embodiment of the present invention to realize the abovestructure is a method for manufacturing a light-emitting deviceincluding the steps of; forming a separation layer over a manufacturingsubstrate having an insulating surface and including a driving circuitportion and a pixel portion; in the driving circuit portion, forming athin film transistor for a driving circuit having an oxide semiconductorlayer over the separation layer; in the pixel portion, forming a thinfilm transistor for a pixel having an oxide semiconductor layer over theseparation layer; forming a first electrode layer electrically connectedto the thin film transistor for a pixel; transferring the thin filmtransistor for a driving circuit, the thin film transistor for a pixel,and the first electrode layer from the manufacturing substrate to asupporting substrate using the separation layer; transferring to aflexible substrate the thin film transistor for a driving circuit, thethin film transistor for a pixel, and the first electrode layer whichhave been transferred to the supporting substrate; forming an EL layerover the first electrode layer which has been transferred to theflexible substrate; forming a second electrode layer over the EL layer;and forming a flexible metal substrate over the second electrode layerso that the driving circuit portion and the pixel portion are sealedwith the flexible metal substrate.

Note that in a photolithography steps in the above-describedmanufacturing process of a light-emitting device, an etching step may beperformed with the use of a mask layer formed using a multi-tone maskwhich is a light-exposure mask through which light is transmitted so asto have a plurality of intensities.

Since a mask layer formed with the use of a multi-tone mask has aplurality of film thicknesses and further can be changed in shape byperforming etching on the mask layer, the mask layer can be used in aplurality of etching steps for processing a film into differentpatterns. Therefore, a mask layer corresponding to at least two kinds ormore of different patterns can be formed by one multi-tone mask. Thus,the number of light-exposure masks can be reduced and the number ofcorresponding photolithography steps can be also reduced, wherebysimplification of the process can be realized.

With the above structure, at least one of the above problems can beresolved.

For example, the oxide semiconductor used in this specification isformed into a thin film represented by InMO₃ (ZnO)_(m)(m>0), and thethin film is used to manufacture a thin film transistor. Note that Mdenotes one metal element or a plurality of metal elements selected fromGa, Fe, Ni, Mn, and Co. As an example, M may be Ga or may include theabove metal element in addition to Ga, such as M may be Ga and Ni or Gaand Fe. Further, in the above oxide semiconductor, in some cases, atransition metal element such as Fe or Ni or an oxide of the transitionmetal is contained as an impurity element in addition to a metal elementcontained as M. In this specification, an oxide semiconductor layerwhose composition formula is represented as InMO₃ (ZnO)_(m) (m>0) wherean oxide semiconductor at least Ga is included as M is referred to as anIn—Ga—Zn—O-based oxide semiconductor, and a thin film thereof is alsoreferred to as an In—Ga—Zn—O-based non-single-crystal film.

As a metal oxide used for the oxide semiconductor layer, any of thefollowing metal oxides can be used in addition to the above: anIn—Sn—Zn—O-based metal oxide; an In—Al—Zn—O-based metal oxide; aSn—Ga—Zn—O-based metal oxide; an Al—Ga—Zn—O-based metal oxide; aSn—Al—Zn—O-based metal oxide; an In—Zn—O-based metal oxide; aSn—Zn—O-based metal oxide; an Al—Zn—O-based metal oxide; an In—O-basedmetal oxide; a Sn—O-based metal oxide; and a Zn—O-based metal oxide.Silicon oxide may be contained in the oxide semiconductor layer formedusing any of the above metal oxides.

The oxide semiconductor preferably includes In, and more preferably, Inand Ga. In order to obtain an i-type (intrinsic) oxide semiconductorlayer, it is effective to perform a dehydration or dehydrogenationprocess.

In the case where heat treatment is performed in an atmosphere of aninert gas such as nitrogen or a rare gas (for example, argon or helium),the oxide semiconductor layer is changed into an oxygen-deficient oxidesemiconductor layer by the heat treatment. Thus, a low-resistant oxidesemiconductor layer, that is, an n-type (such as n-type) oxidesemiconductor layer is formed. Then, the oxide semiconductor layer isbrought into an oxygen-excess state by formation of an oxide insulatingfilm which is in contact with the oxide semiconductor layer and heattreatment after the formation of the oxide insulating film, so that ahigh-resistance oxide semiconductor layer, that is, an i-type oxidesemiconductor layer is formed. This process can also be referred to assolid phase oxidation by which the oxide semiconductor layer is placedin an oxygen-excess state. In this manner, a light-emitting deviceincluding a thin film transistor having high electric characteristicsand high reliability can be manufactured and provided.

For dehydration or dehydrogenation, heat treatment is performed in aninert gas atmosphere of nitrogen or a rare gas (such as argon or helium)at a temperature of 400° C. to 750° C., preferably 420° C. to 570° C.,so that impurities such as moisture included in the oxide semiconductorlayer are reduced. Further, water (H₂O) can be prevented from enteringagain in the oxide semiconductor layer later.

The heat treatment for dehydration or dehydrogenation is preferablyperformed in a nitrogen atmosphere with an H₂O concentration of 20 ppmor lower. Alternatively, the heat treatment may be performed inultra-dry air with an H₂O concentration of 20 ppm or lower.

The oxide semiconductor layer is subjected to heat treatment fordehydration or dehydrogenation under a condition that two peaks of wateror at least one peak of water at around 300° C. is not detected even ifTDS is performed at up to 450° C. on the oxide semiconductor layer afterbeing subjected to dehydration or dehydrogenation. Therefore, even ifTDS is performed at up to 450° C. on a thin film transistor including anoxide semiconductor layer subjected to dehydration or dehydrogenation,at least the peak of water at around 300° C. is not detected.

In addition, when the temperature is lowered from a heating temperatureT at which dehydration or dehydrogenation is performed, it is importantto prevent the dehydrated or dehydrogenated oxide semiconductor layersfrom being exposed to air by continuously using a furnace in whichdehydration or dehydrogenation is performed, so that water or hydrogenis prevented from entering the oxide semiconductor layers. A thin filmtransistor is formed using an oxide semiconductor layer obtained bychanging an oxide semiconductor layer into a low-resistant oxidesemiconductor layer, that is, an n-type (such as n⁻-type) oxidesemiconductor layer by dehydration or dehydrogenation, and then bychanging the low-resistant oxide semiconductor layer into ahigh-resistant oxide semiconductor layer so as to be an i-typesemiconductor layer. In that case, the threshold voltage (Vth) of thethin film transistor can be positive value, so that a so-callednormally-off switching element can be realized. It is desirable for asemiconductor device (a light-emitting device) that a channel be formedwith a threshold voltage that is a positive value and as close to 0 V aspossible. If the threshold voltage of the thin film transistor isnegative, the thin film transistor tends to be a so-called normally on,in other words, a current flows between the source electrode and thedrain electrode even when the gate voltage is 0 V. In an active matrixdisplay device, the electric characteristics of a thin film transistorincluded in a circuit are important and significantly affect theperformance of the display device. A threshold voltage value isspecifically important in the electric characteristics of a thin filmtransistor. In the case where a positive value of the threshold voltageis high or the threshold voltage is a negative value even when thefield-effect mobility is high, it is difficult to control the circuit.Further, in the case of a thin film transistor having a large absolutevalue of the threshold voltage, the thin film transistor cannot performswitching function at low driving voltage and may be a load. In the caseof an n-channel thin film transistor, it is desirable that a channel beformed and a drain current begins to flow only when the positive voltageis applied to a gate. It is unsuitable for a thin film transistor usedin a circuit that a channel is not formed unless driving voltage israised and a channel is formed and a drain current begins to flow evenin a negative voltage state.

Furthermore, the gas atmosphere in which the temperature is lowered fromthe heat temperature T may be switched to a gas atmosphere which isdifferent from the gas atmosphere in which the temperature is raised tothe heat temperature T. For example, cooling is performed while thefurnace used for dehydration or dehydrogenation is filled with ahigh-purity oxygen gas, a high-purity N₂O gas, or an ultra-dry air (witha dew point of −40° C. or lower, preferably −60° C. or lower) withoutexposure to the air.

By using an oxide semiconductor film cooled slowly (or cooled) in anatmosphere that does not contain moisture (with a dew point of −40° C.or lower, preferably −60° C. or lower) after moisture contained in thefilm is reduced by heat treatment for dehydration or dehydrogenation,the electric characteristics of a thin film transistor are improved andhigh-performance thin film transistors that can be mass-produced arerealized.

In this specification, heat treatment in an inert gas atmosphere ofnitrogen or a rare gas (such as argon or helium) is referred to as heattreatment for dehydration or dehydrogenation. In this specification,“dehydrogenation” does not indicate elimination of only H₂ by heattreatment. For convenience, elimination of H, OH, and the like isreferred to as “dehydration or dehydrogenation”.

In the case where heat treatment is performed in an atmosphere of aninert gas such as nitrogen or a rare gas (such as argon or helium), theoxide semiconductor layer is changed into an oxygen-deficient oxidesemiconductor layer by the heat treatment to be a low-resistance oxidesemiconductor layer, that is, an n-type (such as n⁻-type) oxidesemiconductor layer.

Moreover, a region overlapping with the drain electrode layer is formedas a high-resistance drain region (also referred to as an HRD region)which is an oxygen-deficient region. In addition, a region overlappingwith the source electrode layer is formed as a high-resistance sourceregion (also referred to as an HRS region) which is an oxygen-deficientregion.

Specifically, the carrier concentration of the high-resistance drainregion is 1×10¹⁸/cm³ or higher and is at least higher than the carrierconcentration of the channel formation region (less than 1×10¹⁸/cm³).Note that the carrier concentration in this specification refers to avalue of carrier concentration obtained by Hall effect measurement atroom temperature.

The channel formation region is formed by placing at least a part of thedehydrated or dehydrogenated oxide semiconductor layer in anoxygen-excess state to have higher resistance, that is, to become ani-type region. Note that as the treatment for placing the dehydrated ordehydrogenated oxide semiconductor layer in an oxygen-excess state, thefollowing treatment is given: formation of an oxide insulating filmwhich is in contact with the dehydrated or dehydrogenated oxidesemiconductor layer by a sputtering method; heat treatment or heattreatment in an atmosphere including oxygen, or cooling treatment in anoxygen atmosphere or ultra-dry air (having a dew point of −40° C. orlower, preferably −60° C. or lower) after heat treatment in an inert gasatmosphere, after the deposition of the oxide insulating film; or thelike.

Further, in order to use at least a part (a portion overlapping with agate electrode layer) of the dehydrated or dehydrogenated oxidesemiconductor layer as the channel formation region, the oxidesemiconductor layer may be selectively made to be in an oxygen-excessstate so as to be a high-resistance oxide semiconductor layer, that is,an i-type oxide semiconductor layer. The channel formation region can beformed in the following manner: a source electrode layer and a drainelectrode layer formed using metal electrodes of Ti or the like areformed on and in contact with the dehydrated or dehydrogenated oxidesemiconductor layer and exposure regions that do not overlap with thesource electrode layer and the drain electrode layer are selectivelymade to be in an oxygen-excess state. When the exposure regions areselectively made to be in an oxygen-excess state, a firsthigh-resistance source region overlapping with the source electrodelayer and a second high-resistance drain region overlapping with thedrain electrode layer are formed, and a region between the firsthigh-resistance source region and the second high-resistance drainregion serves as the channel formation region. That is, a channel lengthof the channel formation region is formed between the source electrodelayer and the drain electrode layer in a self-aligned manner.

In this manner, a light-emitting device including a thin film transistorhaving high electric characteristics and high reliability can bemanufactured and provided.

Note that by forming the high-resistance drain region in the oxidesemiconductor layer overlapping with the drain electrode layer, thereliability can be improved when a driving circuit is formed.Specifically, by forming the high-resistance drain region, theconductivity can vary stepwise from the drain electrode layer to thehigh-resistance drain region and the channel formation region.Therefore, in the case where the thin film transistor operates with thedrain electrode layer connected to a wiring for supplying a high powersupply potential VDD, the high-resistance drain region serves as abuffer and a high electric field is not applied locally even if a highelectric field is applied between the gate electrode layer and the drainelectrode layer, so that the withstand voltage of the thin filmtransistor can be improved.

In addition, the high-resistance drain region and the high-resistancesource region are formed in the oxide semiconductor layer overlappingwith the drain electrode layer and the source electrode layer,respectively, whereby reduction in leakage current can be achieved inthe channel formation region when forming the driving circuit. Inparticular, by forming the high-resistance drain region, leakage currentflowing between the drain electrode layer and the source electrode layerof the transistor flows through the drain electrode layer, thehigh-resistance drain region on the drain electrode layer side, thechannel formation region, the high-resistance source region on thesource electrode layer side, and the source electrode layer in thisorder. At this time, in the channel formation region, leakage currentflowing from the high-resistance drain region on the drain electrodelayer side to the channel formation region can be concentrated on thevicinity of an interface between the channel formation region and a gateinsulating layer which has high resistance when the transistor is off.Thus, the amount of leakage current in a back channel portion (a part ofa surface of the channel formation region, which is apart from the gateelectrode layer) can be reduced.

Further, the high-resistance source region overlapping with the sourceelectrode layer and the high-resistance drain region overlapping withthe drain electrode layer, although depending on the width of the gateelectrode layer, overlap with each other with a part of the gateelectrode layer and the gate insulating layer interposed therebetween,and the intensity of an electric field in the vicinity of an end portionof the drain electrode layer can be reduced more effectively.

Furthermore, an oxide conductive layer may be formed between the oxidesemiconductor layer and the source and drain electrodes. The oxideconductive layer preferably contains zinc oxide as a component andpreferably does not contain indium oxide. For example, zinc oxide, zincaluminum oxide, zinc aluminum oxynitride, or gallium zinc oxide can beused. The oxide conductive layer also functions as a low-resistancedrain region (LRD, also referred to as an LRN (low-resistance n-typeconductivity) region). Specifically, the carrier concentration of thelow-resistance drain region is higher than that of the high-resistancedrain region (the HRD region) and preferably in a range of 1×10²⁰/cm³ to1×10²¹/cm³. Provision of the oxide conductive layer between the oxidesemiconductor layer and the source and drain electrodes can reducecontact resistance and realizes higher speed operation of thetransistor. Accordingly, frequency characteristics of a peripheralcircuit (a driving circuit) can be improved.

The oxide conductive layer and a metal layer for forming the source anddrain electrodes can be formed in succession.

Moreover, the above-described first wiring and second wiring may beformed using a wiring which is formed by stacking a metal material andthe same material as that of the oxide conductive layer functioning asan LRN or an LRD. By stacking the metal and the oxide conductive layer,coverage at the step such as an overlapping portion of wirings or anopening can be improved; thus, wiring resistance can be lowered.Further, effects of preventing local increase in resistance of a wiringdue to migration or the like and preventing disconnection of a wiringcan be expected; accordingly, a highly reliable light-emitting devicecan be provided.

Regarding the above-described connection between the first wiring andthe second wiring, when the oxide conductive layer is sandwichedtherebetween, it is expected to prevent increase in contact resistancewhich is caused by formation of an insulating oxide on a metal surfacein the connection portion (contact portion); thus, a highly reliablelight-emitting device can be provided.

Since a thin film transistor is easily broken due to static electricityor the like, a protective circuit for protecting the thin filmtransistor for a pixel portion is preferably provided over the samesubstrate as a gate line or a source line. The protective circuit ispreferably formed with a non-linear element including an oxidesemiconductor layer.

Note that the ordinal numbers such as “first” and “second” in thisspecification are used for convenience and do not denote the order ofsteps and the stacking order of layers. In addition, the ordinal numbersin this specification do not denote particular names which specify thepresent invention.

By using an oxide semiconductor layer, a light-emitting device includinga thin film transistor having excellent electric characteristics andhigh reliability can be realized.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 is a view showing a light-emitting device;

FIGS. 2A to 2C are views showing a method for manufacturing alight-emitting device;

FIGS. 3A to 3C are views showing a method for manufacturing alight-emitting device;

FIGS. 4A and 4B are views showing a method for manufacturing alight-emitting device;

FIGS. 5A and 5B are views showing a method for manufacturing alight-emitting device;

FIGS. 6A to 6D are views showing a method for manufacturing alight-emitting device;

FIGS. 7A and 7B are views showing a method for manufacturing alight-emitting device;

FIGS. 8A to 8D are views showing a method for manufacturing alight-emitting device;

FIGS. 9A and 9B are views showing a method for manufacturing alight-emitting device;

FIG. 10 is a view showing a light-emitting device;

FIGS. 11A1, 11A2, 11B1, and 11B2 are views showing a light-emittingdevice;

FIGS. 12A and 12B are block diagrams of a light-emitting device;

FIGS. 13A and 13B are views illustrating a configuration of a signalline driving circuit;

FIGS. 14A to 14D are circuit diagrams showing a configuration of a shiftregister;

FIG. 15A is showing an equivalent circuit of a shift register and 15B istiming charts showing an operation thereof;

FIG. 16 is a view showing a light-emitting device;

FIGS. 17A to 17D are views showing a method for manufacturing alight-emitting device;

FIGS. 18A and 18B are views showing a method for manufacturing alight-emitting device;

FIG. 19 is a view showing a pixel equivalent circuit of a light-emittingdevice;

FIGS. 20A to 20C are views showing a light-emitting device;

FIGS. 21A and 21B are views showing a light-emitting element;

FIGS. 22A and 22B are views showing a light-emitting device;

FIGS. 23A to 23D are views showing an electronic device;

FIG. 24 is a view showing an electronic device;

FIGS. 25A and 25B are views showing an electronic device;

FIG. 26 is a view showing electronic devices;

FIG. 27 is a view showing a light-emitting device;

FIGS. 28A and 28B are views showing a method for manufacturing alight-emitting device;

FIGS. 29A and 29B are views showing a method for manufacturing alight-emitting device; and

FIG. 30 is a view showing a method for manufacturing a light-emittingdevice.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with reference tothe accompanying drawings. Note that the present invention is notlimited to the following description, and various changes for the modesand details thereof will be apparent to those skilled in the art unlesssuch changes depart from the spirit and the scope of the invention.Therefore, the present invention should not be interpreted as beinglimited to the following description of the embodiments. In thestructures to be given below, the same portions or portions havingsimilar functions are denoted by the same reference numerals indifferent drawings, and explanation thereof will not be repeated.

Embodiment 1

A light-emitting device including a thin film transistor and amanufacturing process thereof will be described with reference to FIG.1, FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, FIGS. 5A and 5B, andFIGS. 11A1, 11A2, 11B1, and 11B2.

FIG. 1 shows a light-emitting device which is one mode of the presentinvention. The light-emitting device in FIG. 1 includes, over a flexiblesubstrate 100, a pixel portion including a light-emitting element, athin film transistor 170, and a capacitor 147, and a driving circuitportion including a thin film transistor 180. Further, a first terminal121, a connection electrode 120, and a terminal electrode 128 forconnection are provided in a terminal portion for a gate wiring and asecond terminal 122 and a terminal electrode 129 for connection areprovided in a terminal portion of a source wiring. In addition, an oxideinsulating film 107 and a protective insulating layer 106 are formedover the thin film transistor 180 and the thin film transistor 170.

The light-emitting element is formed using a stack of a first electrodelayer 110, an EL layer 194, and a second electrode layer 195. A drainelectrode layer of the thin film transistor 170 and the first electrodelayer 110 are formed so as to be in contact with each other, so that thelight-emitting element and the thin film transistor 170 are electricallyconnected to each other. In the pixel portion, a color filter layer 191is formed over the protective insulating layer 106. The color filterlayer 191 is covered with an overcoat layer 192, and the protectiveinsulating layer 109 is further formed thereover. The first electrodelayer 110 is formed over the protective insulating layer 109. Further, apartition 193 separating between light-emitting elements is formed overthe thin film transistor 170.

In the thin film transistor 180 of the driving circuit portion, aconductive layer 111 is provided over a gate electrode layer and asemiconductor layer, and a drain electrode layer 165 b is electricallyconnected to a conductive layer 162 which is formed in the same step asthe gate electrode layer.

For the flexible substrate 100, for example, a polyester resin such aspolyethylene terephthalate (PET) or polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, a polyvinylchloride resin, or the like is preferably used.Note that a structure body in which a fibrous body is impregnated withan organic resin (so-called prepreg) may be used as the flexiblesubstrate.

The light-emitting device shown in this embodiment is a bottom emissiontype in which light is emitted through the flexible substrate 100 side,so that a substrate having a light-transmitting property is used as theflexible substrate 100. On the other hand, in the case where thelight-emitting device shown in this embodiment is a top emission type inwhich light emitted through the opposite surface of the flexiblesubstrate 100, a metal substrate which is made thin enough to haveflexibility and does not have light-transmitting properties may be usedas the flexible substrate 100. The metal substrate is formed over a sidethrough which light is not emitted. A material for forming the metalsubstrate is not limited to a particular material, but it is preferableto use aluminum, copper, nickel, an alloy of metal such as an aluminumalloy or stainless steel, or the like.

Hereinafter, a manufacturing method will be described in detail withreference to FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, FIGS. 5Aand 5B, and FIGS. 11A1, 11A2, 11B1, and 11B2. FIGS. 2A to 2C, FIGS. 3Ato 3C, FIGS. 4A and 4B, and FIGS. 5A and 5B each correspond to across-sectional view of the light-emitting device.

A conductive layer is formed over the entire surface of the flexiblesubstrate 100 having an insulating surface, and then a firstphotolithography step is performed to form a resist mask. Unnecessaryportions of the conductive layer are removed by etching to form wiringsand electrodes (a gate electrode layer 101, a gate electrode layer 161,the conductive layer 162, a capacitor wiring layer 108, and the firstterminal 121). Etching is preferably performed so that end portions ofthe wirings and electrodes have tapered shapes as shown in FIG. 2A,because coverage with a film stacked thereover can be improved. Notethat the gate electrode layer 101 and the gate electrode layer 161 areeach included in the gate wiring.

Although there is no particular limitation on a flexible substrate whichcan be used as the flexible substrate 100 having an insulating surface,the flexible substrate needs to have heat resistance enough to withstandat least heat treatment to be performed later.

An insulating film serving as a base film may be provided between theflexible substrate 100, and the gate electrode layer 101, the gateelectrode layer 161, the conductive layer 162, the capacitor wiringlayer 108, and the first terminal 121. The base film has a function ofpreventing diffusion of an impurity element from the flexible substrate100, and can be formed with a single-layer or a stacked-layer using oneor more of a silicon nitride film, a silicon oxide film, a siliconnitride oxide film, and a silicon oxynitride film.

The gate electrode layer 101, the gate electrode layer 161, theconductive layer 162, the capacitor wiring layer 108, and the firstterminal 121 can be formed with a single-layer or a stacked-layer usinga metal material such as molybdenum, titanium, chromium, tantalum,tungsten, aluminum, copper, neodymium, or scandium; or an alloy materialwhich contains any of these materials as a main component.

For example, as a two-layer structure of each of the gate electrodelayer 101, the gate electrode layer 161, the conductive layer 162, thecapacitor wiring layer 108, and the first terminal 121, the followingstructures are preferable: a two-layer structure of an aluminum layerand a molybdenum layer stacked thereover, a two-layer structure of acopper layer and a molybdenum layer stacked thereover, a two-layerstructure of a copper layer and a titanium nitride layer or a tantalumnitride layer stacked thereover, and a two-layer structure of a titaniumnitride layer and a molybdenum layer stacked thereover. As a stackedstructure of layers, a stacked-layer of a tungsten layer or a tungstennitride layer, an alloy of aluminum and silicon or an alloy of aluminumand titanium, and a titanium nitride layer or a titanium layer ispreferable.

Next, a gate insulating layer 102 is formed over the gate electrodelayer 101, the gate electrode layer 161, the conductive layer 162, thecapacitor wiring layer 108, and the first terminal 121 (see FIG. 2A).

The gate insulating layer 102 can be formed to have a single-layer of asilicon oxide layer, a silicon nitride layer, a silicon oxynitridelayer, a silicon nitride oxide layer, or an aluminum oxide layer or astacked-layer thereof by a plasma CVD method, a sputtering method, orthe like. For example, a silicon oxynitride layer may be formed usingSiH₄, oxygen, and nitrogen as a film formation gas by a plasma CVDmethod. The thickness of the gate insulating layer 102 is set to 100 nmto 500 nm. In the case of a stacked structure, for example, a first gateinsulating layer having a thickness from 50 nm to 200 nm and a secondgate insulating layer having a thickness from 5 nm to 300 nm are stackedin this order.

In this embodiment, a silicon oxide layer having a thickness of 200 nmor less is formed by a plasma CVD method as the gate insulating layer102.

Then, an oxide semiconductor film 130 with a thickness of 2 nm to 200 nmis formed over the gate insulating layer 102 (see FIG. 2B).

Note that before the oxide semiconductor film is formed by a sputteringmethod, dust on a surface of the gate insulating layer 102 is preferablyremoved by reverse sputtering in which an argon gas is introduced andplasma is generated. The reverse sputtering is a method in which voltageis applied to a substrate side with the use of an RF power supply in anargon atmosphere without applying voltage to a target side and plasma isgenerated in the vicinity of the substrate so that a substrate surfaceis modified. Note that instead of an argon atmosphere, a nitrogenatmosphere, a helium atmosphere, or the like may be used. Alternatively,an argon atmosphere to which oxygen, N₂O, or the like is added may beused. Further alternatively, an argon atmosphere to which Cl₂, CF₄, orthe like is added may be used.

The oxide semiconductor film 130 is formed using any of the followingfilms: an In—Ga—Zn—O-based non-single-crystal film, an In—Sn—Zn—O-basedoxide semiconductor film, an In—Al—Zn—O-based oxide semiconductor film,a Sn—Ga—Zn—O-based oxide semiconductor film, an Al—Ga—Zn—O-based oxidesemiconductor film, a Sn—Al—Zn—O-based oxide semiconductor film, anIn—Zn—O-based oxide semiconductor film, a Sn—Zn—O-based oxidesemiconductor film, an Al—Zn—O-based oxide semiconductor film, anIn—O-based oxide semiconductor film, a Sn—O-based oxide semiconductorfilm, or a Zn—O-based oxide semiconductor film. In this embodiment, theoxide semiconductor film 130 is formed by a sputtering method with theuse of an In—Ga—Zn—O-based oxide semiconductor target. Alternatively,the oxide semiconductor film 130 can be formed by a sputtering methodunder a rare gas (typically argon) atmosphere, an oxygen atmosphere, oran atmosphere of a rare gas (typically argon) and oxygen. When asputtering method is employed, it is preferable that film formation beperformed using a target containing SiO₂ of 2 wt % to 10 wt % and SiOx(x>0) which inhibits crystallization be contained in the oxidesemiconductor film 130 so as to prevent crystallization at the time ofthe heat treatment for dehydration or dehydrogenation in a later step.

Here, the oxide semiconductor film is formed using an oxidesemiconductor target containing In, Ga, and Zn (In₂O₃:Ga₂O₃:ZnO=1:1:1[mol %], In:Ga:Zn=1:1:0.5 [atom %]) under conditions where the distancebetween the substrate and the target is 100 mm, the pressure is 0.2 Pa,and the direct current (DC) power supply is 0.5 kW in an atmospherecontaining argon and oxygen (argon:oxygen=30 sccm:20 sccm, theproportion of the oxygen flow is 40%). Note that a pulse direct current(DC) power supply is preferable because dust can be reduced and the filmthickness can be uniform. The In—Ga—Zn—O-based non-single-crystal filmis formed to have a thickness of 5 nm to 200 nm. In this embodiment, asthe oxide semiconductor film, an In—Ga—Zn—O-based non-single-crystalfilm having a thickness of 30 nm is formed using the In—Ga—Zn—O-basedoxide semiconductor target by a sputtering method. In addition, as theoxide semiconductor target containing In, Ga, and Zn, a target having acomposition ratio of In:Ga:Zn=1:1:1 [atom %] or In:Ga:Zn=1:1:2 [atom %]can be used.

Examples of a sputtering method include an RF sputtering method in whicha high-frequency power source is used as a sputtering power source, a DCsputtering method in which a DC power source is used as a sputteringpower source, and a pulsed DC sputtering method in which a bias isapplied in a pulsed manner. An RF sputtering method is mainly used inthe case of forming an insulating film, and a DC sputtering method ismainly used in the case of forming a metal film.

Further, there is a multi-source sputtering apparatus in which aplurality of targets of different materials can be set. With themulti-source sputtering apparatus, films of different materials can beformed to be stacked in the same chamber, and a film of plural kinds ofmaterials can be formed by electric discharge at the same time in thesame chamber.

Furthermore, there are a sputtering apparatus provided with a magnetsystem inside the chamber and used for a magnetron sputtering, and asputtering apparatus used for an ECR sputtering in which plasmagenerated with the use of microwaves is used without using glowdischarge.

Moreover, as a film formation method by sputtering, there are also areactive sputtering method in which a target substance and a sputteringgas component are chemically reacted with each other during filmformation to form a thin compound film, and a bias sputtering method inwhich a voltage is also applied to a substrate during film formation.

Next, a second photolithography step is performed. A resist mask 137 isformed over the oxide semiconductor film 130, and unnecessary portionsof the oxide semiconductor film 130 and the gate insulating layer 102are removed by etching to form a contact hole 119 reaching the firstterminal 121 and a contact hole 123 reaching the conductive layer 162 inthe gate insulating layer 102 (see FIG. 2C).

Thus, when the contact holes are formed in the gate insulating layer 102while the oxide semiconductor film 130 is formed over the entire surfaceof the gate insulating layer 102, the resist mask is not in directcontact with the surface of the gate insulating layer 102; accordingly,contamination of the surface of the gate insulating layer 102 (e.g.,attachment of impurities or the like to the gate insulating layer 102)can be prevented. Thus, a favorable state of the interface between thegate insulating layer 102 and the oxide semiconductor film 130 can beobtained, leading to improvement in reliability.

Alternatively, a resist pattern may be formed directly on the gateinsulating layer, and then contact holes may be formed. In such a case,heat treatment is preferably performed to dehydrate or dehydrogenate thesurface of the gate insulating film after removal of the resist. Forexample, impurities such as hydrogen and water included in the gateinsulating layer may be removed by heat treatment (at 400° C. to 750°C.) under an inert gas (e.g., nitrogen, helium, neon, or argon)atmosphere or an oxygen atmosphere.

Next, the resist mask 137 is removed. The oxide semiconductor film 130is etched with the use of resist masks 135 a and 135 b formed in a thirdphotolithography step, so that island-shaped oxide semiconductor layers131 and 132 are formed (see FIG. 3A). Alternatively, the resist masks135 a and 135 b used for forming the island-shaped oxide semiconductorlayers may be formed by an ink-jet method. When the resist masks areformed by an ink-jet method, a photomask is not used, leading toreduction in manufacturing cost.

Next, the oxide semiconductor layers 131 and 132 are subjected todehydration or dehydrogenation, so that dehydrated or dehydrogenatedoxide semiconductor layers 133 and 134 are formed (see FIG. 3B). Thetemperature of first heat treatment at which dehydration ordehydrogenation is performed is 400° C. to 750° C., preferably 425° C.or higher. Note that in the case where the temperature of the first heattreatment is 425° C. or higher, the heat treatment time may be one houror less, while in the case where the temperature of the first heattreatment is lower than 425° C., the heat treatment time is set to morethan one hour. Here, the substrate is introduced into an electricfurnace which is one example of heat treatment apparatuses, and theoxide semiconductor layers are subjected to heat treatment in a nitrogenatmosphere. Then, the oxide semiconductor layers are not exposed to airso as to prevent water and hydrogen from entering the oxidesemiconductor layers again. In this manner, the oxide semiconductorlayers 133 and 134 are formed. In this embodiment, slow cooling isperformed from the heating temperature T at which the oxidesemiconductor layers are dehydrated or dehydrogenated to a temperaturelow enough to prevent water from entering again. Specifically, slowcooling is performed to a temperature that is lower than the heatingtemperature T by 100° C. or more, in a nitrogen atmosphere in onefurnace. Without limitation to a nitrogen atmosphere, dehydration ordehydrogenation may be performed in a rare gas atmosphere such ashelium, neon, or argon.

When the oxide semiconductor layers are subjected to heat treatment at400° C. to 700° C., the dehydration or dehydrogenation of the oxidesemiconductor layers can be achieved; thus, water (H₂O) can be preventedfrom being contained again in the oxide semiconductor layers in latersteps.

Note that the heat treatment apparatus is not limited to the electricfurnace, and for example, an RTA (rapid thermal annealing) apparatussuch as a GRTA (gas rapid thermal annealing) apparatus or an LRTA (lamprapid thermal annealing) apparatus can be used. An LRTA apparatus is anapparatus for heating an object to be processed by radiation of light(an electromagnetic wave) emitted from a lamp such as a halogen lamp, ametal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressuresodium lamp, or a high-pressure mercury lamp. In addition, the LRTAapparatus may be provided with not only a lamp but also a device whichheats an object to be processed by heat conduction or heat radiationfrom a heater such as a resistance heater. GRTA is a method of heattreatment using a high-temperature gas. As the gas, an inert gas whichdoes not react with an object to be processed by heat treatment, forexample, nitrogen or a rare gas such as argon, is used. The heattreatment may be performed by an RTA method at 600° C. to 750° C. forseveral minutes.

Note that in the first heat treatment, it is preferable that water,hydrogen and the like be not contained in nitrogen, or the rare gas suchas helium, neon, or argon. In particular, the heat treatment which isperformed on the oxide semiconductor layers for dehydration ordehydrogenation at 400° C. to 750° C. is preferably performed in anitrogen atmosphere in which the concentration of H₂O is 20 ppm orlower. Alternatively, it is preferable that nitrogen or a rare gas suchas helium, neon, or argon introduced into an apparatus for heattreatment have purity of 6N (99.9999%) or higher, preferably, 7N(99.99999%) or higher; that is, an impurity concentration is set to 1ppm or lower, preferably, 0.1 ppm or lower.

In some cases, the oxide semiconductor layers are crystallized to bemicrocrystalline films or polycrystalline films depending on theconditions of the first heat treatment or the material of the oxidesemiconductor layers. For example, the oxide semiconductor layers maycrystallize to become microcrystalline semiconductor layers having adegree of crystallization of 90% or more, or 80% or more. Further,depending on the conditions of the first heat treatment and the materialof the oxide semiconductor layers, the oxide semiconductor layers maybecome amorphous oxide semiconductor layers containing no crystallinecomponent. Furthermore, in some cases, the oxide semiconductor filmbecame an amorphous oxide film in which a microcrystal portion (thegrain size of the microcrystal portion is 1 nm to 20 nm (typically, 2 nmto 4 nm)) is mixed. When high temperature heat treatment is performedusing RTA (GRTA, LRTA), needle-like crystals might be generatedlongitudinally (in the film thickness direction) on the surface side ofthe oxide semiconductor film.

The first heat treatment of the oxide semiconductor layer can also beperformed on the oxide semiconductor film 130 which has not beenprocessed into the island-shaped oxide semiconductor layers 131 and 132.In that case, after the first heat treatment, the substrate is taken outof the heating device and a photolithography step is performed.

The heat treatment for dehydration or dehydrogenation of the oxidesemiconductor layers may be performed at any of the following timings:after the oxide semiconductor layers are formed; after a sourceelectrode and a drain electrode are formed over the oxide semiconductorlayer; and after a passivation film is formed over the source electrodeand the drain electrode.

Further, the step of forming the contact holes 123 and 119 in the gateinsulating layer 102 as shown in FIG. 2C may be performed after theoxide semiconductor film 130 is subjected to dehydration ordehydrogenation treatment.

Note that this etching step of the oxide semiconductor film is notlimited to wet etching and dry etching may also be performed.

As the etching gas for dry etching, a gas containing chlorine(chlorine-based gas such as chlorine (Cl₂), boron chloride (BCl₃),silicon chloride (SiCl₄), or carbon tetrachloride (CCl₄)) is preferablyused.

Alternatively, a gas containing fluorine (fluorine-based gas such ascarbon tetrafluoride (CF₄), sulfur fluoride (SF₆), nitrogen fluoride(NF₃), or trifluoromethane (CHF₃)); hydrogen bromide (HBr); oxygen (O₂);any of these gases to which a rare gas such as helium (He) or argon (Ar)is added; or the like can be used.

As the dry etching method, a parallel plate RIE (reactive ion etching)method or an ICP (inductively coupled plasma) etching method can beused. In order to etch the films into desired shapes, the etchingcondition (the amount of electric power applied to a coil-shapedelectrode, the amount of electric power applied to an electrode on asubstrate side, the temperature of the electrode on the substrate side,or the like) is adjusted as appropriate.

As an etchant used for wet etching, a solution obtained by mixingphosphoric acid, acetic acid, nitric acid, or the like can be used. Inaddition, ITO-07N (produced by KANTO CHEMICAL CO., INC.) may also beused.

The etchant used in the wet etching is removed by cleaning together withthe material which is etched off. The waste liquid including the etchantand the material etched off may be purified and the material may bereused. When a material such as indium included in the oxidesemiconductor layer is collected from the waste liquid after the etchingand reused, the resources can be efficiently used and the cost can bereduced.

The etching conditions (such as an etchant, etching time, andtemperature) are adjusted as appropriate depending on the material sothat the material can be etched into a desired shape.

Next, a metal conductive film is formed using a metal material over theoxide semiconductor layers 133 and 134 by a sputtering method or avacuum evaporation method.

As a material of the metal conductive film, there are an elementselected from Al, Cr, Cu, Ta, Ti, Mo, or W, an alloy including the aboveelement, an alloy film in which some of the above elements are combined,and the like. Further, the metal conductive film may have a single-layerstructure or a stacked-layer structure of two or more layers. Forexample, a single-layer structure of an aluminum film including silicon,a two-layer structure of an aluminum film and a titanium film stackedthereover, a three-layer structure in which a Ti film, an aluminum film,and a Ti film are stacked in this order, and the like can be given.Alternatively, a film, an alloy film, or a nitride film which containsaluminum (Al) and one or a plurality of elements selected from titanium(Ti), tantalum (Ta), tungsten (W), molybdenum (Mo), chromium (Cr),neodymium (Nd), and scandium (Sc) may be used.

In the case where heat treatment is performed after formation of themetal conductive film, the metal conductive film preferably has heatresistance enough to withstand the heat treatment.

Next, a fourth photolithography step is performed. Resist masks 136 a,136 b, 136 c, 136 d, 136 e, 136 f, and 136 g are formed, and unnecessaryportions of the metal conductive film are removed by etching, so that asource electrode layer 105 a, a drain electrode layer 105 b, a sourceelectrode layer 165 a, the drain electrode layer 165 b, a capacitorelectrode layer 149, the connection electrode 120, and the secondterminal 122 are formed (see FIG. 3C).

Note that each material and etching conditions are adjusted asappropriate so that the oxide semiconductor layers 133 and 134 are notremoved when the metal conductive film is etched.

In this embodiment, a Ti film is used as the metal conductive film, anIn—Ga—Zn—O-based is used as the oxide semiconductor layers 133 and 134,and an ammonia hydrogen peroxide solution (a mixture of ammonia, water,and a hydrogen peroxide solution) is used as an etchant.

In the fourth photolithography step, the connection electrode 120 andthe second terminal 122, which are formed using the same material asthat of the source electrode layers 105 a and 165 a and the drainelectrode layers 105 b and 165 b, are formed in the respective terminalportions. Note that the second terminal 122 is electrically connected toa source wiring (a source wiring including the source electrode layers105 a and 165 a). The connection electrode 120 is formed in contact withthe first terminal 121 in the contact hole 119 and electricallyconnected to the first terminal 121.

Note that the resist masks 136 a, 136 b, 136 c, 136 d, 136 e, 136 f, and136 g used for forming the source electrode layers and the drainelectrode layers may be formed by an ink-jet method. When the resistmasks are formed by an ink-jet method, a photomask is not used, leadingto reduction in manufacturing cost.

Next, the resist masks 136 a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136g are removed, and an oxide insulating film 107 serving as a protectiveinsulating film in contact with the oxide semiconductor layers 133 and134 is formed.

At this stage, in the oxide semiconductor layers 133 and 134, there areregions in contact with the oxide insulating film. Among these regions,the regions in which the gate electrode layers overlap with the oxideinsulating film 107 with the gate insulating layer interposedtherebetween are channel formation regions.

The oxide insulating film 107 can be formed to have a thickness of atleast 1 nm or more by a sputtering method or the like, as appropriate,which is a method with which impurities such as water and hydrogen, arenot mixed into the oxide insulating film 107. In this embodiment, asilicon oxide film with a thickness of 300 nm is formed as the oxideinsulating film 107 by a sputtering method. The substrate temperature infilm formation may be room temperature to 300° C. In this embodiment,the substrate temperature is at room temperature. The silicon oxide filmcan be formed by a sputtering method in a rare gas (typically argon)atmosphere, an oxygen atmosphere, or an atmosphere including a rare gas(typically argon) and oxygen. Further, a silicon oxide target or asilicon target can be used as a target. For example, a silicon oxide canbe formed by a sputtering method using a silicon target in an atmosphereof oxygen and nitrogen. As the oxide insulating film which is formed incontact with the oxide semiconductor layer whose resistance is reduced,an inorganic insulating film which does not include impurities such asmoisture, a hydrogen ion, and OH⁻ and blocks entry of these from theoutside is used. Typically, a silicon oxide film, a silicon nitrideoxide film, an aluminum oxide film, or an aluminum oxynitride film isused.

Next, second heat treatment is performed in an inert gas atmosphere or anitrogen atmosphere (at a preferable temperature from 200° C. to 400°C., e.g., from 250° C. to 350° C.). For example, the second heattreatment is performed in a nitrogen atmosphere at 250° C. for one hour.By the second heat treatment, part of the oxide semiconductor layers 133and 134 which overlaps with the oxide insulating film 107 is heated inthe state of being in contact with the oxide insulating film 107.

Through the above-described steps, heat treatment for dehydration ordehydrogenation is performed on the oxide semiconductor layer after filmformation to reduce the resistance, and then, part of the oxidesemiconductor layer is selectively made to be in an oxygen-excess state.

As a result, in the oxide semiconductor layer 133, a channel formationregion 166 overlapping with the gate electrode layer 161 becomes ani-type channel formation region, and a high-resistance source region 167a overlapping with the source electrode layer 165 a and ahigh-resistance drain region 167 b overlapping with the drain electrodelayer 165 b are formed in a self-aligned manner; thus, an oxidesemiconductor layer 163 is formed. Similarly, in the oxide semiconductorlayer 134, a channel formation region 116 overlapping with the gateelectrode layer 101 becomes an i-type channel formation region, and ahigh-resistance source region 117 a overlapping with the sourceelectrode layer 105 a and a high-resistance drain region 117 boverlapping with the drain electrode layer 105 b are formed in aself-aligned manner; thus, an oxide semiconductor layer 103 is formed.

By formation of the high-resistance drain regions 117 b and 167 b (orthe high-resistance source regions 117 a and 167 a) in the oxidesemiconductor layers 103 and 163 which overlap with the drain electrodelayers 105 b and 165 b (and the source electrode layers 105 a and 165a), respectively, reliability in a formed circuit can be improved.Specifically, by forming the high-resistance drain region 117 b, theconductivity can vary stepwise from the drain electrode layer 105 b tothe high-resistance drain region 117 b and the channel formation region116; similarly, by formation of the high-resistance drain region 167 b,the conductivity can vary stepwise from the drain electrode layer 165 bto the high-resistance drain region 167 b and the channel formationregion 166. Therefore, when the transistors operate in the state ofbeing connected to a wiring which supplies the drain electrode layers105 b and 165 b with a high power source potential VDD, thehigh-resistance drain regions serve as buffers and a high electric fieldis not applied locally even if a high electric field is applied betweenthe gate electrode layers 101 and 161 and the drain electrode layers 105b and 165 b, so that the withstand voltage of the transistor can beimproved.

In addition, by formation of the high-resistance drain regions 117 b and167 b (or the high-resistance source regions 117 a and 167 a) in theoxide semiconductor layers 103 and 163 which overlap with the drainelectrode layers 105 b and 165 b (and the source electrode layers 105 aand 165 a), respectively, leakage current in the channel formationregions 116 and 166 which may flow in a formed circuit can be reduced.

In this embodiment, after a silicon oxide film is formed by a sputteringmethod as the oxide insulating film 107, heat treatment is performed at250° C. to 350° C., whereby oxygen enters each of the oxidesemiconductor layers from the exposed portion (the channel formationregion) of the oxide semiconductor layer between the source region andthe drain region, and is diffused thereinto. By formation of the siliconoxide film by a sputtering method, an excessive amount of oxygen can becontained in the silicon oxide film, and oxygen can enter the oxidesemiconductor layers and can be diffused thereinto through the heattreatment. Oxygen enters the oxide semiconductor layers and is diffusedthereinto, whereby the channel region can have higher resistance (suchas i-type conductivity). Thus, normally-off thin film transistors can beobtained.

Further, the high-resistance source region or the high-resistance drainregion in the oxide semiconductor layer is formed in the entirethickness direction in the case where the thickness of the oxidesemiconductor layer is 15 nm or smaller. In the case where the thicknessof the oxide semiconductor layer is 30 nm to 50 nm, in part of the oxidesemiconductor layer, that is, in a region in the oxide semiconductorlayer which is in contact with the source electrode layer or the drainelectrode layer and the vicinity thereof, resistance is reduced. Then, ahigh-resistance source region or a high-resistance drain region isformed, while a region in the oxide semiconductor layer, which is closeto the gate insulating film, can be made to be an i-type region.

Furthermore, the heat treatment may be performed at 100° C. to 200° C.for one hour to 30 hours in an air atmosphere. In this embodiment, theheat treatment is performed at 150° C. for 10 hours. This heat treatmentmay be performed at a fixed heating temperature. Alternatively, thefollowing change in the heating temperature may be conducted pluraltimes repeatedly: the heating temperature is increased from a roomtemperature to a temperature of 100° C. to 200° C. and then decreased toa room temperature. In addition, this heat treatment may be performedbefore formation of the oxide insulating film under a reduced pressure.Under the reduced pressure, the heat treatment time can be shortened.With such heat treatment, hydrogen is introduced from the oxidesemiconductor layers to the oxide insulating layer; thus, normally-offthin film transistors can be obtained. Therefore, reliability of thesemiconductor device can be improved.

A protective insulating layer may be additionally formed over the oxideinsulating film 107. For example, a silicon nitride film is formed by anRF sputtering method. Since an RF sputtering method has highproductivity, it is preferably used as a film formation method of theprotective insulating layer. As the protective insulating layer, aninorganic insulating film which does not include impurities such asmoisture, a hydrogen ion, and OH⁻ and blocks entry of these from theoutside is used. Specifically, a silicon nitride film, an aluminumnitride film, a silicon nitride oxide film, an aluminum oxynitride film,or the like is used. In this embodiment, a silicon nitride film isformed as the protective insulating layer 106 (see FIG. 4A).

Through the above steps, the transistor 180 in the driving circuitportion, the thin film transistor 170 in the pixel portion, and thecapacitor 147 can be manufactured over one substrate. Each of the thinfilm transistors 170 and 180 is a bottom-gate thin film transistorincluding an oxide semiconductor layer in which a high-resistance sourceregion, a high-resistance drain region, and a channel formation regionare formed. Therefore, in each of the thin film transistors 170 and 180,the high-resistance drain region or the high-resistance source regionserves as a buffer and a high electric field is not applied locally evenif a high electric field is applied, so that the withstand voltage ofthe transistor can be improved.

The capacitor 147 is formed using the gate insulating layer 102, thecapacitor wiring layer 108, and the capacitor electrode layer 149, inwhich the gate insulating layer 102 in the capacitor portion is used asa dielectric.

By providing the driving circuit and the pixel portion over the samesubstrate, connection wirings between the driving circuit and anexternal signal can be shortened; thus, reduction in size and cost ofthe light-emitting device can be achieved.

Then, the color filter layer 191 is formed over the protectiveinsulating layer 106. As the color filter layer, a green color filterlayer, a blue color filter layer, a red color filter layer, or the likecan be used, and a green color filter layer, a blue color filter, and ared color filter layer are sequentially formed. Each color filter layeris formed by a printing method, an ink-jet method, an etching methodwith the use of a photolithography technique, or the like. By providingthe color filter layers, alignment of the color filter layers andlight-emitting regions of light-emitting elements can be performedwithout depending on the attachment accuracy of the sealing substrate.In this embodiment, fifth, sixth, and seventh photolithography steps areperformed to form a green color filter layer, a blue color filter layer,and a red color filter layer.

Next, an overcoat layer 192 which covers the color filter layers (thegreen color filter layer, the blue color filter layer, and the red colorfilter layer) is formed. The overcoat layer 192 is formed using alight-transmitting resin. In this embodiment, the overcoat layer 192 isformed in an eighth photolithography step.

Here, an example in which full color display is performed using threecolors of RGB is shown; however, the invention is not particularlylimited thereto, and full color display may be performed using fourcolors of RGBW.

Next, a protective insulating layer 109 which covers the overcoat layer192 and the protective insulating layer 106 is formed (see FIG. 4B). Forthe protective insulating layer 109, an inorganic insulating film suchas a silicon nitride film, an aluminum nitride film, a silicon nitrideoxide film, or an aluminum oxynitride film is used. It is preferablethat the protective insulating layer 109 be an insulating film havingthe same component as that of the protective insulating layer 106because they can be etched in one step when contact holes are formed.

Next, a ninth photolithography step is performed. A resist mask isformed, and a contact hole 125 which reaches the drain electrode layer105 b is formed by etching the oxide insulating film 107, the protectiveinsulating layer 106, and the protective insulating layer 109. Then, theresist mask is removed (see FIG. 5A). In addition, a contact hole 127which reaches the second terminal 122 and a contact hole 126 whichreaches the connection electrode 120 are also formed by this etching.Alternatively, a resist mask for forming the contact holes may be formedby an ink-jet method. A photomask is not used when the resist mask isformed by an ink-jet method, leading to reduction in manufacturing cost.

Next, a light-transmitting conductive film is formed. Thelight-transmitting conductive film is formed using a material such asindium oxide (In₂O₃) or an alloy of indium oxide and tin oxide(In₂O₃—SnO₂, abbreviated to ITO) by a sputtering method, a vacuumevaporation method, or the like. Alternatively, an Al—Zn—O-basednon-single-crystal film containing nitrogen (i.e., an Al—Zn—O—N-basednon-single-crystal film), a Zn—O-based non-single-crystal filmcontaining nitrogen, or a Sn—Zn—O-based non-single-crystal filmcontaining nitrogen may be used as the material of thelight-transmitting conductive film. Note that the composition ratio(atomic %) of zinc in the Al—Zn—O—N-based non-single-crystal film is 47atomic % or lower and is higher than that of aluminum in thenon-single-crystal film; the composition ratio (atomic %) of aluminum inthe Al—Zn—O—N-based non-single-crystal film is higher than that ofnitrogen in the non-single-crystal film. Such a material is etched witha hydrochloric acid-based solution. However, since a residue is easilyleft on the substrate particularly in etching ITO, an alloy of indiumoxide and zinc oxide (In₂O₃—ZnO) may be used in order to improve etchingprocessability.

Note that the unit of the composition ratio in the light-transmittingconductive film is atomic percent (atomic %), and the composition ratiois evaluated by analysis using an electron probe X-ray microanalyzer(EPMA).

Next, a tenth photolithography step is performed. A resist mask isformed, and unnecessary portions of the light-transmitting conductivefilm are removed by etching, so that the first electrode layer 110, theconductive layer 111, and the terminal electrodes 128 and 129 areformed. Then, the resist mask is removed.

The capacitor 147, which includes the gate insulating layer 102 as adielectric, the capacitor wiring layer 108, and the capacitor electrodelayer 149, can also be formed over the same substrate as the drivingcircuit portion and the pixel portion. In a light-emitting device, thecapacitor electrode layer 149 is part of a power supply line, and thecapacitor wiring layer 108 is part of a gate electrode layer of adriving TFT.

The terminal electrodes 128 and 129 which are formed in the terminalportion function as electrodes or wirings connected to an FPC. Theterminal electrode 128 formed over the first terminal 121 with theconnection electrode 120 interposed therebetween is a connectionterminal electrode serving as an input terminal for the gate wiring. Theterminal electrode 129 formed over the second terminal 122 is aconnection terminal electrode serving as an input terminal for thesource wiring.

Further, FIGS. 11A1 and 11A2 are a cross-sectional view of a gate wiringterminal portion at this stage and a top view thereof, respectively.FIG. 11A1 is a cross-sectional view taken along line C1-C2 in FIG. 11A2.In FIG. 11A1, a conductive film 155 formed over the oxide insulatingfilm 107 is a connection terminal electrode serving as an inputterminal. Furthermore, in FIG. 11A1, in the terminal portion, a firstterminal 151 formed using the same material as that of the gate wiringand a connection electrode 153 formed using the same material as that ofthe source wiring overlap with each other with the gate insulating layer102 interposed therebetween, and are electrically connected to eachother. In addition, the connection electrode 153 and the conductive film155 are in direct contact with each other through a contact holeprovided in the oxide insulating film 107 to form conductiontherebetween.

Further, FIGS. 11B1 and 11B2 are a cross-sectional view of a sourcewiring terminal portion at this stage and a top view thereof,respectively. FIG. 11B1 corresponds to a cross-sectional view takenalong line D1-D2 in FIG. 11B2. In FIG. 11B1, the conductive film 155formed over the oxide insulating film 107 is a connection terminalelectrode serving as an input terminal. Furthermore, in FIG. 11B1, inthe terminal portion, an electrode 156 formed using the same material asthat of the gate wiring is located below and overlapped with the secondterminal 150, which is electrically connected to the source wiring, withthe gate insulating layer 102 interposed therebetween. The electrode 156is not electrically connected to the second terminal 150, and acapacitor for preventing noise or static electricity can be formed whenthe potential of the electrode 156 is set to a potential different fromthat of the second terminal 150, such as floating, GND, or 0 V. Thesecond terminal 150 is electrically connected to the conductive film 155with the oxide insulating film 107 interposed therebetween.

A plurality of gate wirings, source wirings, and capacitor wirings areprovided depending on the pixel density. In the terminal portion, thefirst terminal at the same potential as the gate wiring, the secondterminal at the same potential as the source wiring, the third terminalat the same potential as the capacitor wiring, and the like are eacharranged in plurality. The number of each of the terminals may be anynumber, and the number of the terminals may be determined by apractitioner as appropriate.

The thin film transistors and the storage capacitor are arranged inmatrix in respective pixels so that a pixel portion is formed, which canbe used as one of substrates for manufacturing an active matrix displaydevice. In this specification, such a substrate is referred to as anactive matrix substrate for convenience.

The conductive layer 111 is provided so as to overlap with the channelformation region 166 in the oxide semiconductor layer, whereby in abias-temperature stress test (hereinafter, referred to as a BT test) forexamining the reliability of a thin film transistor, the amount ofchange in threshold voltage of the thin film transistor 180 before andafter the BT test can be reduced. A potential of the conductive layer111 may be the same as or different from that of the gate electrodelayer 161. The conductive layer 111 can also serve as a second gateelectrode layer. Alternatively, the potential of the conductive layer111 may be GND or 0 V, or the conductive layer 111 may be in a floatingstate.

Next, a partition 193 is formed so as to cover the periphery portion ofthe first electrode layer 110. The partition 193 is formed using a filmof an organic resin such as polyimide, acrylic, polyamide, or epoxy, aninorganic insulating film, or a siloxane-based resin.

Note that the siloxane-based resin corresponds to a resin including aSi—O—Si bond formed using a siloxane-based material as a startingmaterial. The siloxane-based resin may include, as a substituent, anorganic group (e.g., an alkyl group or an aryl group) or a fluoro group.In addition, the organic group may include a fluoro group.

The partition 193 can be formed using phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), or the like. Note that the partition193 may be formed by stacking a plurality of insulating films formedusing any of these materials.

There is no particular limitation on the method for forming thepartition 193. The partition 193 can be formed, depending on thematerial, with a method such as a sputtering method, an SOG method, aspin coating method, a dipping method, a spray coating method, or adroplet discharge method (e.g., an ink-jet method, screen printing, oroffset printing), or with a means such as a doctor knife, a roll coater,a curtain coater, or a knife coater. Further, other insulating layersused in the light-emitting device may be formed using the materials andthe methods which are shown as examples of the materials and the methodsof the partition 193.

It is particularly preferable that the partition 193 be formed using aphotosensitive resin material to have an opening portion over the firstelectrode layer 110 so that a sidewall of the opening portion is formedas a tilted surface with continuous curvature. When the partition 193 isformed using a photosensitive resin material, a step for forming aresist mask can be omitted. In this embodiment, an eleventhphotolithography steps is performed, so that the partition 193 isformed.

The EL layer 194 is formed over the first electrode layer 110 and thesecond electrode layer 195 is formed over the EL layer 194, whereby alight-emitting element is formed. Note that the second electrode layer195 is electrically connected to a common potential line. Any of avariety of materials can be used for the second electrode layer 195.Specifically, the second electrode layer 195 is preferably formed usinga material having a low work function, for example, an alkali metal suchas Li or Cs; an alkaline earth metal such as Mg, Ca, or Sr; an alloycontaining any of these metals (e.g., Mg:Ag or Al:Li); or a rare earthmetal such as Yb or Er. In this embodiment, an aluminum film is used asthe second electrode layer 195.

Through these eleven photolithography steps with the use of the elevenphotomasks, the light-emitting device of this embodiment shown in FIG. 1can be manufactured, which includes the driving circuit portion havingthe thin film transistor 180, the pixel portion having the thin filmtransistor 170 and the light-emitting element, the capacitor 147 havingthe storage capacitor, and an external extraction terminal portion.

Further, in this embodiment, an example where the contact holes in theoxide insulating film 107, the protective insulating layer 106, and theprotective insulating layer 109 are formed in one photolithography stepis described; however, contact holes may be formed in a plurality ofphotolithography steps with different photomasks. For example, the fifthphotolithography step may be performed to form contact holes in theoxide insulating film 107 and the protective insulating layer 106serving as interlayer insulating layers, the sixth to ninthphotolithography steps may be performed to form the RGB color filterlayers and the overcoat layer, and then contact holes may be formed inthe protective insulating layer 109 in the tenth photolithography step.In this case, the number of photolithography steps and photomasksincreases by one; accordingly, the light-emitting device is formedthrough the twelve photolithography steps with twelve photomasks.

Note that in the above-described photolithography steps, an etching stepmay be performed with the use of a mask layer formed using a multi-tonemask which is a light-exposure mask through which light is transmittedso as to have a plurality of intensities.

Since a mask layer formed with the use of a multi-tone mask has aplurality of film thicknesses and can be changed shapes thereof byperforming etching on the mask layer, the mask layer can be used in aplurality of etching steps for processing into different patterns.Therefore, a mask layer corresponding at least two kinds or more ofdifferent patterns can be formed by one multi-tone mask. Thus, thenumber of light-exposure masks can be reduced and the number ofcorresponding photolithography steps can also be reduced, wherebysimplification of a process can be realized.

Further, when a light-emitting device is manufactured, a power supplyline electrically connected to the source electrode layer of the drivingTFT is provided. The power supply line intersects with a gate wiring anda source wiring and is formed using the same material and in the samestep as the gate electrode layer.

Furthermore, in the case where a light-emitting device is manufactured,one electrode of the light-emitting element is electrically connected tothe drain electrode layer of the driving TFT, and a common potentialline which is electrically connected to the other electrode of thelight-emitting element is provided. Note that the common potential linecan be formed using the same material and in the same step as the gateelectrode layer.

Moreover, in the case where a light-emitting device is manufactured, aplurality of thin film transistors are provided in one pixel, and aconnection portion which connects the gate electrode layer of one thinfilm transistor to the drain electrode layer of the other thin filmtransistor is provided.

The use of an oxide semiconductor for a thin film transistor leads toreduction in manufacturing cost. In particular, an oxide insulating filmis formed in contact with an oxide semiconductor layer by the abovemethod, whereby a thin film transistor having stable electriccharacteristics can be manufactured and provided. Therefore, alight-emitting device which includes highly reliable thin filmtransistors having favorable electric characteristics can be provided.

The channel formation region in the semiconductor layer is ahigh-resistance region; thus, electric characteristics of the thin filmtransistor are stabilized and increase in off current or the like can beprevented. Therefore, a light-emitting device including a highlyreliable thin film transistor having favorable electric characteristicscan be provided.

Since a thin film transistor is easily broken due to static electricityor the like, a protective circuit is preferably provided over the samesubstrate as the pixel portion or the driving circuit. The protectivecircuit is preferably formed with a non-linear element including anoxide semiconductor layer. For example, protective circuits are providedbetween the pixel portion and a scan line input terminal and between thepixel portion and a signal line input terminal. In this embodiment, aplurality of protective circuits are provided so that the pixeltransistor and the like are not broken when surge voltage due to staticelectricity or the like is applied to a scan line, a signal line, and acapacitor bus line. Therefore, the protective circuit is formed so as torelease charge to a common wiring when surge voltage is applied to theprotective circuit. Further, the protective circuit includes non-linearelements arranged in parallel to the scan line. The non-linear elementincludes a two-terminal element such as a diode or a three-terminalelement such as a transistor. For example, the non-linear element canalso be formed through the same step as the thin film transistor 170 inthe pixel portion, and can be made to have the same properties as adiode by connecting a gate terminal to a drain terminal of thenon-linear element.

This embodiment can be implemented in appropriate combination with thestructures described in the other embodiments.

Embodiment 2

In this embodiment, an example in which oxide conductive layers areprovided as a source region and a drain region between the oxidesemiconductor layer and the source and drain electrode layers inEmbodiment 1 will be described with reference to FIGS. 6A to 6D andFIGS. 7A and 7B. Therefore, part of this embodiment can be performed ina manner similar to that of Embodiment 1; thus, repetitive descriptionof the same portions as or portions having functions similar to those inEmbodiment 1 and steps for forming such portions will be omitted. SinceFIGS. 6A to 6D and FIGS. 7A and 7B are the same as FIG. 1, FIGS. 2A to2C, FIGS. 3A to 3C, FIGS. 4A and 4B, and FIGS. 5A and 5B except for partof steps, the same portions are denoted by the same reference numeralsand detailed description of the same portions is omitted.

First, the steps up to and including the step in FIG. 3B in Embodiment 1are performed in accordance with Embodiment 1. FIG. 6A shows the samestep as FIG. 3B.

An oxide conductive film 140 is formed over the dehydrated ordehydrogenated oxide semiconductor layers 133 and 134, and a metalconductive film formed using a metal conductive material is stacked overthe oxide conductive film 140.

As a film formation method of the oxide conductive film 140, asputtering method, a vacuum evaporation method (e.g., an electron beamevaporation method), an arc discharge ion plating method, or a spraymethod is used. A material of the oxide conductive film 140 preferablycontains zinc oxide as a component and preferably does not containindium oxide. For such an oxide conductive film 140, zinc oxide,aluminum zinc oxide, aluminum zinc oxynitride, gallium zinc oxide, orthe like can be used. The thickness of the oxide conductive film isselected as appropriate in the range of 50 nm to 300 nm. In addition, inthe case where a sputtering method is used, it is preferable that filmformation be performed using a target containing SiO₂ at 2 wt % or moreto 10 wt % or less, and SiO_(x) (x>0), which inhibits crystallization,be contained in the oxide conductive film so that crystallization issuppressed when the heat treatment for dehydration or dehydrogenation isperformed in a later step.

Next, a fourth photolithography step is performed. The resist masks 136a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136 g are formed. Then,unnecessary portions of the metal conductive film are removed byetching, whereby the source electrode layer 105 a, the drain electrodelayer 105 b, the source electrode layer 165 a, the drain electrode layer165 b, the capacitor electrode layer 149, the connection electrode 120,and the second terminal 122 are formed (see FIG. 6B).

Note that each material and etching conditions are adjusted asappropriate so that the oxide conductive film 140 and the oxidesemiconductor layers 133 and 134 are not removed in etching of the metalconductive film.

Next, the resist masks 136 a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136g are removed. The oxide conductive film 140 is etched using the sourceelectrode layer 105 a, the drain electrode layer 105 b, the sourceelectrode layer 165 a, and the drain electrode layer 165 b as masks, sothat oxide conductive layers 164 a and 164 b, oxide conductive layers104 a and 104 b, and a capacitor electrode layer 185 are formed (seeFIG. 6C). The oxide conductive film 140 containing zinc oxide as acomponent can be easily etched with an alkaline solution such as aresist stripping solution, for example. In addition, oxide conductivelayers 138 and 139 are also formed in respective terminal portions inthis step.

Etching treatment for dividing the oxide conductive layer to formchannel formation regions is performed by utilizing the difference inetching rates between the oxide semiconductor layers and the oxideconductive layer. The oxide conductive layer over the oxidesemiconductor layers is selectively etched utilizing a higher etchingrate of the oxide conductive film as compared to that of the oxidesemiconductor layers.

Therefore, removal of the resist masks 136 a, 136 b, 136 c, 136 d, 136e, 136 f, and 136 g is preferably performed by an ashing process. In thecase of etching with a stripping solution, etching conditions (the kindof the etchant, the concentration, and the etching time) are adjusted asappropriate so that the oxide conductive film 140 and the oxidesemiconductor layers 133 and 134 are not etched excessively.

As described in this embodiment, after forming the island-shaped oxidesemiconductor layers by etching, the oxide conductive film and the metalconductive film are stacked thereover, and etching is performed usingthe same masks to form a wiring pattern including source electrodelayers and drain electrode layers, oxide conductive films can be leftunder the wiring pattern of the metal conductive film.

At the contact portion between the gate wiring (the conductive layer162) and the source wiring (the drain electrode layer 165 b), the oxideconductive layer 164 b is formed below the source wiring. The oxideconductive layer 164 b serves as a buffer, the resistance is only theseries resistance depending on the thickness of the oxide conductivelayer, and further the oxide conductive layer 164 b does not form aninsulating oxide with metal, which is preferable.

Next, the oxide insulating film 107 serving as a protective insulatingfilm is formed in contact with the oxide semiconductor layer 133 and134. In this embodiment, a silicon oxide film with a thickness of 300 nmis formed as the oxide insulating film 107 by a sputtering method.

Next, second heat treatment is performed in an inert gas atmosphere or anitrogen atmosphere at a preferable temperature from 200° C. to 400° C.,e.g., from 250° C. to 350° C. For example, the second heat treatment isperformed in a nitrogen atmosphere at 250° C. for one hour. By thesecond heat treatment, part of the oxide semiconductor layers 133 and134 which overlaps with the oxide insulating film 107 is heated in thestate of being in contact with the oxide insulating film 107.

Through the above steps, heat treatment for dehydration ordehydrogenation is performed on the oxide semiconductor layer after filmformation to reduce the resistance, and then, part of the oxidesemiconductor layer is selectively made to be in an oxygen-excess state.

As a result, in the oxide semiconductor layer 133, a channel formationregion 166 overlapping with the gate electrode layer 161 becomes ani-type channel formation region, and a high-resistance source region 167a overlapping with the source electrode layer 165 a and the oxideconductive layer 164 a, and a high-resistance drain region 167 boverlapping with the drain electrode layer 165 b and the oxideconductive layer 164 b are formed in a self-aligned manner; thus, anoxide semiconductor layer 163 is formed. Similarly, in the oxidesemiconductor layer 134, a channel formation region 116 overlapping withthe gate electrode layer 101 becomes an i-type channel formation region,and a high-resistance source region 117 a overlapping with the sourceelectrode layer 105 a and the oxide conductive layer 104 a, and ahigh-resistance drain region 117 b overlapping with the drain electrodelayer 105 b and the oxide conductive layer 164 b are formed in aself-aligned manner; thus, an oxide semiconductor layer 103 is formed.

The oxide conductive layers 104 b and 164 b which are provided betweenthe oxide semiconductor layers 103 and 163 and the drain electrodelayers 105 b and 165 b formed using a metal material, each also functionas a low-resistance drain (LRD, also referred to as an LRN(low-resistance n-type conductivity)) region. Similarly, the oxideconductive layers 104 a and 164 a which are provided between the oxidesemiconductor layers 103 and 163 and the source electrode layers 105 aand 165 a formed using a metal material, each also function as alow-resistance source (LRS, also referred to as an LRN (low-resistancen-type conductivity)) region. With the structure including the oxidesemiconductor layer, the low-resistance drain region, and the drainelectrode layer formed using a metal material, withstand voltage of thetransistor can be further increased. Specifically, the carrierconcentration of the low-resistance drain region is higher than that ofthe high-resistance drain region (the HRD region) and preferably in arange of 1×10²⁰/cm³ or higher and 1×10²¹/cm³ or lower.

Through the above steps, a thin film transistor 171 in the pixel portionand a transistor 181 in the driving circuit portion can be manufacturedover the same substrate. Each of the thin film transistors 171 and 181is a bottom-gate thin film transistor including an oxide semiconductorlayer in which a high-resistance source region, a high-resistance drainregion, and a channel formation region are formed. Therefore, in each ofthe thin film transistors 172 and 181, the high-resistance drain regionor the high-resistance source region serves as a buffer and a highelectric field is not applied locally even if a high electric field isapplied, so that the withstand voltage of the transistor can beimproved.

In the capacitor portion, a capacitor 146 is formed from a stack of thecapacitor wiring layer 108, the gate insulating layer 102, the capacitorelectrode layer 185 formed in the same step as the oxide conductivelayer 104 b, and the capacitor electrode layer 149 formed in the samestep as the drain electrode layer 105 b.

Next, the protective insulating layer 106 is formed over the oxideinsulating film 107 and the color filter layer 191 is formed over theprotective insulating layer 106 in the pixel portion. The overcoat layer192 is formed so as to cover the color filter layer 191 and theprotective insulating layer 109 is formed so as to cover the protectiveinsulating layer 106 and the overcoat layer 192.

Next, a ninth photolithography step is performed in a manner similar tothat performed in Embodiment 1. A resist mask is formed, and the contacthole 125 which reaches the drain electrode layer 105 b is formed byetching the oxide insulating film 107, the protective insulating layer106, and the protective insulating layer 109. Then, the resist mask isremoved (see FIG. 6D). In addition, the contact hole 127 which reachesthe second terminal 122 and the contact hole 126 which reaches theconnection electrode 120 are also formed by this etching.

Next, a light-transmitting conductive film is formed, and a tenthphotolithography step is performed. A resist mask is formed andunnecessary portions of the light-transmitting conductive film areremoved by etching to form the first electrode layer 110, the conductivelayer 111, and the terminal electrodes 128 and 129. Then, the resistmasks are removed (see FIG. 7A).

As in Embodiment 1, the partition 193 is formed in an eleventhphotolithography step. The EL layer 194 and the second electrode layer195 are stacked over the first electrode layer 110, so that thelight-emitting device of this embodiment which includes a light-emittingelement is manufactured (see FIG. 7B).

When the oxide conductive layers are provided between the oxidesemiconductor layer and the source and drain electrode layers as thesource region and the drain region, the source region and the drainregion can have lower resistance and the transistor can operate at highspeed. It is effective to use the oxide conductive layers for a sourceregion and a drain region in order to improve frequency characteristicsof a peripheral circuit (a driving circuit). This is because the contactbetween a metal electrode (e.g., Ti) and an oxide conductive layer canreduce the contact resistance as compared to the contact between a metalelectrode (e.g., Ti) and an oxide semiconductor layer.

There has been a problem in that molybdenum (Mo) which is used as a partof a wiring material (e.g., Mo/Al/Mo) in a light-emitting device hashigh contact resistance with an oxide semiconductor layer. This isbecause Mo is less likely to be oxidized and has a weaker effect ofextracting oxygen from the oxide semiconductor layer as compared totitanium (Ti), and a contact interface between Mo and the oxidesemiconductor layer is not changed to have n-type conductivity. However,even in such a case, the contact resistance can be reduced byinterposing an oxide conductive layer between the oxide semiconductorlayer and source and drain electrode layers; accordingly, frequencycharacteristics of a peripheral circuit (a driving circuit) can beimproved.

The channel length of the thin film transistor is determined at the timeof etching the oxide conductive layer; accordingly, the channel lengthcan be further shortened. For example, the channel length L can be setas small as 0.1 μm to 2 μm; in this way, operation speed can beincreased.

Embodiment 3

In this embodiment, another example in which oxide conductive layers areprovided as a source region and a drain region between the oxidesemiconductor layer and the source and drain electrode layers inEmbodiment 1 or 2 will be described with reference to FIGS. 8A to 8D andFIGS. 9A and 9B. Therefore, part of this embodiment can be performed ina manner similar to that of Embodiment 1 or 2; thus, repetitivedescription of the same portions as or portions having functions similarto those in Embodiment 1 or 2 and steps for forming such portions willbe omitted. Since FIGS. 8A to 8D and FIGS. 9A and 9B are the same asFIG. 1, FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, FIGS. 5A and5B, FIGS. 6A to 6D, and FIGS. 7A and 7B except for part of steps, thesame portions are denoted by the same reference numerals and detaileddescription of the same portions is omitted.

First, in accordance with Embodiment 1, a metal conductive film isformed over the substrate 100, and the metal conductive film is etchedusing a resist mask formed in a first photolithography step, so that thefirst terminal 121, the gate electrode layer 161, the conductive layer162, the gate electrode layer 101, and the capacitor wiring layer 108are formed.

Next, the gate insulating layer 102 is formed over the first terminal121, the gate electrode layer 161, the conductive layer 162, the gateelectrode layer 101, and the capacitor wiring layer 108, and then anoxide semiconductor film and an oxide conductive film are stacked. Thegate insulating layer, the oxide semiconductor film, and the oxideconductive film can be formed in succession without being exposed toair.

Resist masks are formed over the oxide conductive film in a secondphotolithography step. The gate insulating layer, the oxidesemiconductor film, and the oxide conductive film are etched using theresist masks to form the contact hole 119 which reaches the firstterminal 121 and the contact hole 123 which reaches the conductive layer162.

The resist masks formed in the second photolithography step are removed,and resist masks are newly formed over the oxide conductive film in athird photolithography step. With the use of the resist masks in thethird photolithography step, island-shaped oxide semiconductor layersand island-shaped oxide conductive layers are formed.

When the contact holes are formed in the gate insulating layer in thestate where the oxide semiconductor film and the oxide conductive filmare stacked over the entire surface of the gate insulating layer in sucha manner, the resist masks are not directly in contact with the surfaceof the gate insulating layer; accordingly, contamination of the surfaceof the gate insulating layer (e.g., attachment of impurities or the liketo the gate insulating layer) can be prevented. Thus, a favorable stateof the interfaces between the gate insulating layer and the oxidesemiconductor film and between the gate insulating layer and the oxideconductive film can be obtained, whereby reliability can be improved.

Next, heat treatment for dehydration or dehydrogenation is performed inthe state where the oxide semiconductor layers and the oxide conductivelayers are stacked. By the heat treatment at 400° C. to 700° C., thedehydration or dehydrogenation of the oxide semiconductor layers can beachieved; thus, water (H₂O) can be prevented from being contained againin the oxide semiconductor layers in later steps.

As long as a substance which inhibits crystallization such as siliconoxide is not contained in the oxide conductive layers, the oxideconductive layers are crystallized through this heat treatment. Crystalof the oxide conductive layers grows in a columnar shape with respect toa base surface. Accordingly, when the metal conductive film formed overthe oxide conductive layers is etched in order to form a sourceelectrode layer and a drain electrode layer, formation of an undercutcan be prevented.

Further, by the heat treatment for dehydration or dehydrogenation of theoxide semiconductor layers, conductivity of the oxide conductive layerscan be improved. Note that only the oxide conductive layers may besubjected to heat treatment at a temperature lower than that for theoxide semiconductor layers.

In addition, in the case where the separation layer is formed and thenthe thin film transistor and the light-emitting element are formed overthe manufacturing substrate, the heat treatment for dehydration ordehydrogenation allows separation at an interface of the separationlayer to be easily performed from the manufacturing substrate to asupporting substrate in a later process.

The first heat treatment of the oxide semiconductor layers and the oxideconductive layers can also be performed on the oxide semiconductor filmand the oxide conductive film which have not been processed intoisland-shaped oxide semiconductor layers and the island-shaped oxideconductive layers. In that case, after the first heat treatment, thesubstrate is taken out of the heating device, and then aphotolithography step is performed.

Through the above steps, the oxide semiconductor layers 133 and 134 andoxide conductive layers 142 and 143 can be obtained (see FIG. 8A). Theoxide semiconductor layer 133 and the oxide conductive layer 142 areisland-shaped stacked-layers formed using the same mask, and the oxidesemiconductor layer 134 and the oxide conductive layer 143 areisland-shaped stacked-layers formed using the same mask.

Next, a fourth photolithography step is performed. The resist masks 136a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136 g are formed, andunnecessary portions of the metal conductive film are removed byetching, so that the source electrode layer 105 a, the drain electrodelayer 105 b, the source electrode layer 165 a, the drain electrode layer165 b, the capacitor electrode layer 149, the connection electrode 120,and the second terminal 122 are formed (see FIG. 8B).

Note that each material and etching conditions are adjusted asappropriate so that the oxide conductive layers 142 and 143 and theoxide semiconductor layers 133 and 134 are not removed in etching of themetal conductive film.

Next, the resist masks 136 a, 136 b, 136 c, 136 d, 136 e, 136 f, and 136g are removed. Then the oxide conductive layers 142 and 143 are etchedusing the source electrode layer 105 a, the drain electrode layer 105 b,the source electrode layer 165 a, and the drain electrode layer 165 b asmasks, so that the oxide conductive layers 164 a and 164 b and the oxideconductive layers 104 a and 104 b are formed (see FIG. 8C). The oxideconductive layers 142 and 143 containing zinc oxide as a component canbe easily etched with an alkaline solution such as a resist strippingsolution, for example.

Therefore, removal of the resist masks 136 a, 136 b, 136 c, 136 d, 136e, 136 f, and 136 g is preferably performed by an ashing process. In thecase of etching with a stripping solution, etching conditions (the kindof the etchant, the concentration, and the etching time) are adjusted asappropriate so that the oxide conductive layers 142 and 143 and theoxide semiconductor layers 133 and 134 are not etched excessively.

Next, the oxide insulating film 107 serving as a protective insulatingfilm is formed in contact with the oxide semiconductor layer 133 and134. In this embodiment, a silicon oxide film with a thickness of 300 nmis formed as the oxide insulating film 107 by a sputtering method.

Next, second heat treatment is performed in an inert gas atmosphere or anitrogen atmosphere at a preferable temperature from 200° C. to 400° C.,e.g., from 250° C. to 350° C. For example, the second heat treatment isperformed in a nitrogen atmosphere at 250° C. for one hour. By thesecond heat treatment, part of the oxide semiconductor layers 133 and134 which overlaps with the oxide insulating film 107 is heated in thestate of being in contact with the oxide insulating film 107.

Through the above steps, heat treatment for dehydration ordehydrogenation is performed on the oxide semiconductor layer after filmformation to reduce the resistance. Then, part of the oxidesemiconductor layer is selectively made to be in an oxygen-excess state.

As a result, in the oxide semiconductor layer 133, a channel formationregion 166 overlapping with the gate electrode layer 161 becomes ani-type channel formation region, and a high-resistance source region 167a overlapping with the source electrode layer 165 a and the oxideconductive layer 164 a, and a high-resistance drain region 167 boverlapping with the drain electrode layer 165 b and the oxideconductive layer 164 b are formed in a self-aligned manner; thus, anoxide semiconductor layer 163 is formed. Similarly, in the oxidesemiconductor layer 134, a channel formation region 116 overlapping withthe gate electrode layer 101 becomes an i-type channel formation region,and a high-resistance source region 117 a overlapping with the sourceelectrode layer 105 a and the oxide conductive layer 104 a, and ahigh-resistance drain region 117 b overlapping with the drain electrodelayer 105 b and the oxide conductive layer 164 b are formed in aself-aligned manner; thus, an oxide semiconductor layer 103 is formed.

The oxide conductive layers 104 b and 164 b which are provided betweenthe oxide semiconductor layers 103 and 163 and the drain electrodelayers 105 b and 165 b formed using a metal material, each also functionas a low-resistance drain (LRD, also referred to as an LRN) region.Similarly, the oxide conductive layers 104 a and 164 a which areprovided between the oxide semiconductor layers 103 and 163 and thesource electrode layers 105 a and 165 a formed using a metal material,each also function as a low-resistance source (LRS, also referred to asan LRN) region. With the structure including the oxide semiconductorlayer, the low-resistance drain region, and the drain electrode layerformed using a metal material, withstand voltage of the transistor canbe further increased. Specifically, the carrier concentration of thelow-resistance drain region is higher than that of the high-resistancedrain region (the HRD region) and preferably in a range of 1×10²⁰/cm³ to1×10²¹/cm³.

Through the above steps, a thin film transistor 172 in the pixel portionand a transistor 182 in the driving circuit portion can be manufacturedover the same substrate. Each of the thin film transistors 172 and 181is a bottom-gate thin film transistor including an oxide semiconductorlayer in which a high-resistance source region, a high-resistance drainregion, and a channel formation region are formed. Therefore, in each ofthe thin film transistors 172 and 181, the high-resistance drain regionor the high-resistance source region serves as a buffer and a highelectric field is not applied locally even if a high electric field isapplied, so that the withstand voltage of the transistor can beimproved.

Further, in the capacitor portion, the capacitor 147 is formed from astack of the capacitor wiring layer 108, the gate insulating layer 102,and the capacitor electrode layer 149 formed in the same step as thedrain electrode layer 105 b.

Next, the protective insulating layer 106 is formed over the oxideinsulating film 107. In the pixel portion, the color filter layer 191 isformed over the protective insulating layer 106. The overcoat layer 192is formed so as to cover the color filter layer 191. Then, theprotective insulating layer 109 is formed so as to cover the protectiveinsulating layer 106 and the overcoat layer 192.

Next, a ninth photolithography step is performed in a manner similar tothat performed in Embodiment 1. A resist mask is formed, and the contacthole 125 which reaches the drain electrode layer 105 b is formed byetching the oxide insulating film 107, the protective insulating layer106, and the protective insulating layer 109. Then, the resist mask isremoved (see FIG. 8D). In addition, the contact hole 127 which reachesthe second terminal 122 and the contact hole 126 which reaches theconnection electrode 120 are also formed by this etching.

Next, a light-transmitting conductive film is formed, and a tenthphotolithography step is performed. A resist mask is formed andunnecessary portions of the light-transmitting conductive film areremoved by etching to form the first electrode layer 110, the conductivelayer 111, and the terminal electrodes 128 and 129. Then, the resistmasks are removed (see FIG. 9A).

As in Embodiment 1, the partition 193 is formed in an eleventhphotolithography step. The EL layer 194 and the second electrode layer195 are stacked over the first electrode layer 110, so that thelight-emitting device of this embodiment which includes a light-emittingelement is manufactured (see FIG. 9B).

When the oxide conductive layers are provided between the oxidesemiconductor layer and the source and drain electrode layers as thesource region and the drain region, the source region and the drainregion can have lower resistance and the transistor can operate at highspeed. It is effective to use the oxide conductive layers for a sourceregion and a drain region in order to improve frequency characteristicsof a peripheral circuit (a driving circuit). This is because the contactresistance between a metal electrode (e.g., Ti) and an oxide conductivelayer is lower than the contact resistance between a metal electrode(e.g., Ti) and an oxide semiconductor layer.

The contact resistance can be reduced by interposing the oxideconductive layers between the oxide semiconductor layer and the sourceand drain electrode layers; accordingly, frequency characteristics of aperipheral circuit (a driving circuit) can be improved.

The channel length of the thin film transistor is determined at the timeof etching the oxide conductive layer; accordingly, the channel lengthcan be further shortened. For example, the channel length L can be setas small as 0.1 μm to 2 μm; in this way, operation speed can beincreased.

Embodiment 4

In this embodiment, an example of a light-emitting device in Embodiment1, in which a thin film transistor in a pixel portion and a firstelectrode layer of a light-emitting element are electrically connectedto each other through a connection electrode layer will be describedwith reference to FIG. 16, FIGS. 17A to 17D, and FIGS. 18A and 18B.Therefore, part of this embodiment can be performed in a manner similarto that of Embodiment 1; thus, repetitive description of the sameportions as or portions having functions similar to those in Embodiment1 and steps for forming such portions will be omitted. Since FIG. 16,FIGS. 17A to 17D, and FIGS. 18A and 18B are the same as FIG. 1, FIGS. 2Ato 2C, FIGS. 3A to 3C, FIGS. 4A and 4B, and FIGS. 5A and 5B except forpart of steps, the same portions are denoted by the same referencenumerals and detailed description of the same portions is omitted.

FIG. 16 shows a light-emitting device of this embodiment. The drainelectrode layer 105 b of the thin film transistor 170 in the pixelportion is electrically connected to the first electrode layer 110through a connection electrode layer 196. A method for manufacturing thelight-emitting device illustrated in FIG. 16 will be described withreference to FIGS. 17A to 17D and FIGS. 18A and 18B.

First, according to Embodiment 1, the steps up to and including the stepin FIG. 4A in Embodiment 1 are performed. FIG. 17A illustrates the samestep as FIG. 4A.

Next, a fifth photolithography step is performed. A resist mask isformed, and the contact hole 125 which reaches the drain electrode layer105 b, the contact hole 127 which reaches the second terminal 122, andthe contact hole 126 which reaches the connection electrode 120 areformed by etching the oxide insulating film 107 and the protectiveinsulating layer 106. Then, the resist mask is removed (see FIG. 17B).

Next, a conductive film is formed, and a sixth photolithography step isperformed. A resist mask is formed and unnecessary portions of theconductive film are removed by etching to form the connection electrodelayer 196, a conductive layer 112, and terminal electrodes 113 and 114.Then, the resist masks are removed (see FIG. 17C). As the conductivefilm, a metal conductive film can be used; therefore, the connectionelectrode layer 196, the conductive layer 112, and the terminalelectrodes 113 and 114 can be formed of a metal conductive layer.

As the connection electrode layer 196, a film including an elementselected from Al, Cr, Cu, Ta, Ti, Mo, and W as its main component or astacked film including a film of any of the elements and an alloy filmthereof can be used. Accordingly, in the case where the conductive layer112 and the terminal electrodes 113 and 114 are formed in the same stepas the connection electrode layer 196 as in this embodiment, theconductive layer 112 and the terminal electrodes 113 and 114 can also beformed using a film including an element selected from Al, Cr, Cu, Ta,Ti, Mo, and W as its main component or a stacked film including a filmof any of the elements and an alloy film thereof. The conductive film isnot limited to a single-layer including the above element and can beformed in a stacked-layer of two or more layers. As a film formationmethod of the conductive film, a sputtering method, a vacuum evaporationmethod (e.g., an electron beam evaporation method), an arc discharge ionplating method, or a spray method can be used.

Next, the color filter layer 191 is formed over the protectiveinsulating layer 106 in the pixel portion in seventh to ninthphotolithography steps and the overcoat layer 192 is formed so as tocover the color filter layer 191 in a tenth photolithography step. Theprotective insulating layer 109 is formed so as to cover the connectionelectrode layer 196, the conductive layer 112, the terminal electrodes113 and 114, the protective insulating layer 106, and the overcoat layer192 (see FIG. 17D).

Next, an eleventh photolithography step is performed. A resist mask isformed, and the contact hole 125 which reaches the connection electrodelayer 196 is formed by etching the protective insulating layer 109.Then, the resist mask is removed. In addition, the protective insulatinglayer 109 over the terminal electrodes 113 and 114 is also removed bythis etching, so that the terminal electrodes 113 and 114 are exposed(see FIG. 18A).

Then, a light-transmitting conductive film is formed. A twelfthphotolithography step is performed. A resist mask is formed andunnecessary portions of the light-transmitting conductive film areetched to form the first electrode layer 110. Then, the resist mask isremoved.

As in Embodiment 1, the partition 193 is formed in a thirteenthphotolithography step. The EL layer 194 and the second electrode layer195 are stacked over the first electrode layer 110; thus, thelight-emitting device of this embodiment, which includes alight-emitting element, is manufactured (see FIG. 18B).

In the case where the connection electrode layer 196 is formed, a powersupply line can be formed using the same material as and in the samestep as the connection electrode layer 196. Further, a common potentialline can also be formed using the same material as and in the same stepas the connection electrode layer 196.

This embodiment can be implemented in appropriate combination with anyof the structures described in Embodiments 1 to 3.

Embodiment 5

In this embodiment, FIG. 10 shows an example of a thin film transistorwhose manufacturing process is partly different from that ofEmbodiment 1. FIG. 10 is the same as FIG. 1, FIGS. 2A to 2C, FIGS. 3A to3C, FIGS. 4A and 4B, and FIGS. 5A and 5B except for part of the steps.Thus, the same parts as in FIG. 1, FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS.4A and 4B, and FIGS. 5A and 5B are denoted by the same referencenumerals and detailed description on the parts is omitted.

First, according to Embodiment 1, the gate electrode layer and the gateinsulating layer are formed over a substrate. Then, in the pixelportion, a contact hole which reaches the gate electrode layer is formedin a second photolithography step (not shown).

Next, the oxide semiconductor film 130 is formed and then processed intothe island-shaped oxide semiconductor layers 131 and 132 in a thirdphotolithography step.

Next, the oxide semiconductor layers 131 and 132 are dehydrated ordehydrogenated. The temperature of first heat treatment at whichdehydration or dehydrogenation is performed is 400° C. to 750° C.,preferably 425° C. or higher. Note that in the case where thetemperature of the first heat treatment is 425° C. or higher, the heattreatment time may be one hour or less, while in the case where thetemperature of the first heat treatment is lower than 425° C., the heattreatment time is set to more than one hour. Here, the substrate isintroduced into an electric furnace which is one example of heattreatment apparatuses, and the oxide semiconductor layers are subjectedto heat treatment in a nitrogen atmosphere. Then, the oxidesemiconductor layers are not exposed to air so as to prevent water andhydrogen from entering the oxide semiconductor layers again. In thismanner, oxide semiconductor layers are obtained. Then, a high-purityoxygen gas, a high-purity N₂O gas, or ultra-dry air (having a dew pointof −40° C. or lower, preferably −60° C. or lower) is introduced to thesame furnace and cooling is performed. It is preferable that water,hydrogen, or the like be not contained in the oxygen gas or the N₂O gas.Alternatively, it is preferable that the oxygen gas or the N₂O gas,which is introduced into an apparatus for heat treatment, have purity of6N (99.9999%) or more, preferably 7N (99.99999%) or more; that is, animpurity concentration in the oxygen gas or the N₂O gas is preferably 1ppm or lower, further preferably 0.1 ppm or lower.

Note that the heat treatment apparatus is not limited to the electricfurnace, and, for example, an RTA (rapid thermal annealing) apparatussuch as a GRTA (gas rapid thermal annealing) apparatus or an LRTA (lamprapid thermal annealing) apparatus can be used. An LRTA apparatus is anapparatus for heating an object to be processed by radiation of light(an electromagnetic wave) emitted from a lamp such as a halogen lamp, ametal halide lamp, a xenon arc lamp, a carbon arc lamp, a high-pressuresodium lamp, or a high-pressure mercury lamp. In addition, the LRTAapparatus may be provided with not only a lamp but also a device whichheats an object to be processed by heat conduction or heat radiationfrom a heater such as a resistance heater. GRTA is a method of heattreatment using a high-temperature gas. As the gas, an inert gas whichdoes not react with an object to be processed by heat treatment, forexample, nitrogen or a rare gas such as argon, is used. The heattreatment may be performed by an RTA method at 600° C. to 750° C. forseveral minutes.

Further, after the first heat treatment for dehydration ordehydrogenation, heat treatment may be performed at 200° C. to 400° C.,preferably 200° C. to 300° C., in an oxygen gas atmosphere or an N₂O gasatmosphere.

Furthermore, the first heat treatment of the oxide semiconductor layers131 and 132 can also be performed on the oxide semiconductor film 130which has not been processed into the island-shaped oxide semiconductorlayers. In that case, after the first heat treatment, the substrate istaken out of the heating device and a photolithography step isperformed.

Through the above process, the entire region of the oxide semiconductorfilm is made in an oxygen-excess state, thereby having higherresistance; accordingly, oxide semiconductor layers 168 and 118 whichare entirely intrinsic are obtained.

Next, a fourth photolithography step is performed. Resist masks areformed over the oxide semiconductor layers 168 and 118 and a sourceelectrode layer and a drain electrode layer are formed by a selectiveetching. An oxide insulating film 107 is formed by a sputtering method.

Next, in order to reduce variation in electric characteristics of thethin film transistors, heat treatment (preferably 150° C. to lower than350° C.) may be performed in an inert gas atmosphere or a nitrogen gasatmosphere. For example, heat treatment may be performed under anitrogen atmosphere at 250° C. for an hour.

Next, the protective insulating layer 106 is formed over the oxideinsulating film 107. In the pixel portion, the color filter layer 191 isformed over the protective insulating layer 106. The overcoat layer 192is formed so as to cover the color filter layer 191 and the protectiveinsulating layer 109 is formed so as to cover the protective insulatinglayer 106 and the overcoat layer 192.

Next, a ninth photolithography step is performed. A resist mask isformed and contact holes which reach the first terminal 121, theconductive layer 162, the drain electrode layer 105 b, and the secondterminal 122 are formed by etching the gate insulating layer 102, theoxide insulating film 107, the protective insulating layer 106, and theprotective insulating layer 109. After a light-transmitting conductivefilm is formed, a tenth photolithography step is performed. Resist masksare formed and selective etching is performed to form the firstelectrode layer 110, the terminal electrode 128, the terminal electrode129, and a wiring layer 145.

This embodiment is an example where the first terminal 121 and theterminal electrode 128 are directly connected to each other without theconnection electrode 120. Further, the drain electrode layer 165 b andthe conductive layer 162 are connected to each other through the wiringlayer 145.

In the capacitor portion, the capacitor 147 is formed from a stack ofthe capacitor wiring layer 108, the gate insulating layer 102, and thecapacitor electrode layer 149 formed in the same step as the sourceelectrode layer and the drain electrode layer.

Through the above steps, a thin film transistor 183 in the drivingcircuit portion and a thin film transistor 173 in a pixel portion can beformed over one substrate.

As in Embodiment 1, the partition 193 is formed and the EL layer 194 andthe second electrode layer 195 are stacked over the first electrodelayer 110, whereby the light-emitting device of this embodiment, whichincludes a light-emitting element, is manufactured (see FIG. 10).

This embodiment can be implemented in appropriate combination with anyof the structures described in Embodiments 1 to 4.

Embodiment 6

This embodiment shows an example of a manufacturing method for alight-emitting device by separating a thin film transistor from amanufacturing substrate and transferring the thin film transistor to aflexible substrate. A light-emitting device, one embodiment of thepresent invention, is described using FIG. 27, FIGS. 28A and 28B, FIGS.29A and 29B, and FIG. 30. FIG. 27 shows an example of the light-emittingdevice described in this embodiment. Note that this embodiment is thesame as Embodiment 1 except part of the process; thus, the same portionsare denoted by the same reference numerals, and detailed description ofthe same portions is omitted.

A light-emitting device 8400 has a pixel portion 8250, a driving circuitportion 8252, and terminal portions 8254 and 8255. The pixel portion8250 and the driving circuit portion 8252 are formed between a firstsubstrate 8100 which is thin, lightweight and has a light-transmittingproperty, and a second substrate 8144 which is thin and has low waterpermeability. In addition, the pixel portion 8250 and the drivingcircuit portion 8252 are held between a resin layer 8141 touching thefirst substrate 8100 and a resin layer 8142 touching the secondsubstrate 8144.

The pixel portion 8250 has the thin film transistor 170, and alight-emitting element including the first electrode layer 110, the ELlayer 194, and the second electrode layer 195. Further, one of a sourceelectrode and a drain electrode of the thin film transistor 170 isconnected to the first electrode layer 110 of the light-emittingelement. Note that the partition 193 is provided to cover a part of thefirst electrode layer 110. The pixel portion 8250 has the capacitor 147.

The driving circuit portion 8252 has the thin film transistor 180.

A summary of the manufacturing method for the light-emitting device 8400shown as an example in this embodiment is as follows. First, as a layerto be separated, the terminal portions of the light-emitting device8400, the thin film transistor 170, the thin film transistor 180, thecapacitor 147, the color filter layer 191, the overcoat layer 192, theoxide insulating film 107, the protective insulating layer 106, theprotective insulating layer 109, and the first electrode layer 110 ofthe light-emitting element are formed over a separation layer of a firstmanufacturing substrate. Next, after the layer to be separated istemporarily bonded to a second manufacturing substrate (also referred toas a support substrate), the layer to be separated is separated from thefirst manufacturing substrate. Then, the layer to be separated is bondedand transferred to the first substrate 8100 which is thin, lightweightand has a light-transmitting property, and the second manufacturingsubstrate which is temporarily bonded is removed from the layer to beseparated. Then, after forming a light-emitting element over the firstelectrode layer 110 exposed on the surface of the layer to be separated,the second substrate 8144 which is thin and has low water permeabilityis bonded to a surface of the layer to be separated on which thelight-emitting element is formed, so that the light-emitting device 8400is manufactured.

An example of the manufacturing method for the light-emitting device8400 is described in detail with reference to FIGS. 28A and 28B, FIGS.29A and 29B, and FIG. 30.

A separation layer 302 is formed over a first manufacturing substrate300 and a first insulating layer 8104 is formed over the separationlayer 302. Preferably, the first insulating layer 8104 is successivelyformed without exposing the formed separation layer 302 to air. Thissuccessive formation prevents dust or impurities from entering betweenthe separation layer 302 and the insulating layer 8104.

As the first manufacturing substrate 300, a glass substrate, a quartzsubstrate, a sapphire substrate, a ceramic substrate, a metal substrate,or the like can be used. Alternatively, a plastic substrate having heatresistance to the processing temperature of this embodiment may be used.In the manufacturing process of a semiconductor device, a manufacturingsubstrate can be selected as appropriate in accordance with the process.

Further, when the temperature of heat treatment performed later is high,a substrate having a strain point of 730° C. or higher is preferablyused as the glass substrate. For a glass substrate, a glass materialsuch as aluminosilicate glass, aluminoborosilicate glass, or bariumborosilicate glass is used, for example. By containing more barium oxide(BaO) than boric acid, a more practical heat-resistant glass substratecan be obtained. Therefore, a glass substrate containing BaO more thanB₂O₃ is preferably used. Furthermore, crystallized glass or the like canbe used.

Note that in this process, the separation layer 302 is formed on anentire surface of the first manufacturing substrate 300; however, afterforming the separation layer 302 on the entire surface of the firstmanufacturing substrate 300, the separation layer 302 may be selectivelyremoving so that the separation layer can be formed only on a desiredregion, if needed. Further, the separation layer 302 is formed incontact with the first manufacturing substrate 300 in FIGS. 28A and 28B,though an insulating layer can be formed between the first manufacturingsubstrate 300 and the separation layer 302 using a silicon oxide film, asilicon oxynitride film, a silicon nitride film, a silicon nitride oxidefilm, or the like, if needed.

The separation layer 302 has a single-layer structure or a stacked-layerstructure containing an element selected from tungsten (W), molybdenum(Mo), titanium (Ti), tantalum (Ta), niobium (Nb), nickel (Ni), cobalt(Co), zirconium (Zr), ruthenium (Ru), rhodium (Rh), palladium (Pd),osmium (Os), iridium (Ir), or silicon (Si); or an alloy materialcontaining any of the elements as its main component; a compoundmaterial containing any of the elements as its main component. Acrystalline structure of a layer containing silicon may be any of anamorphous structure, a microcrystalline structure, and a polycrystallinestructure.

The separation layer 302 can be formed by a sputtering method, a plasmaCVD method, a coating method, a printing method, or the like. Note thatthe coating method includes a spin coating method, a droplet dischargemethod, and a dispensing method.

In the case where the separation layer 302 has a single-layer structure,a tungsten layer, a molybdenum layer, or a layer containing a mixture oftungsten and molybdenum is preferably formed. Alternatively, a layercontaining an oxide or an oxynitride of tungsten, a layer containing anoxide or an oxynitride of molybdenum, or a layer containing an oxide oran oxynitride of a mixture of tungsten and molybdenum is formed. Notethat the mixture of tungsten and molybdenum corresponds to an alloy oftungsten and molybdenum, for example.

In the case where the separation layer 302 has a stacked-layerstructure, as a first layer, a tungsten layer, a molybdenum layer, or alayer containing a mixture of tungsten and molybdenum is preferablyformed. As a second layer, an oxide of tungsten, molybdenum, or amixture of tungsten and molybdenum; a nitride of tungsten, molybdenum,or a mixture of tungsten and molybdenum; an oxynitride of tungsten,molybdenum, or a mixture of tungsten and molybdenum; or a nitride oxideof tungsten, molybdenum, or a mixture of tungsten and molybdenum ispreferably formed.

In the case where the stacked-layer structure of a layer containingtungsten and a layer containing an oxide of tungsten is formed as theseparation layer 302, the following manner may be utilized: the layercontaining tungsten is formed, and an insulating layer formed using anoxide is formed over the layer containing tungsten, whereby the layercontaining an oxide of tungsten is formed in the interface between thetungsten layer and the insulating layer.

In addition, in the case where the separation layer is formed and thenthe thin film transistor and the light-emitting element are formed overthe manufacturing substrate, the separation layer is heated by heattreatment for dehydration or dehydrogenation of an oxide semiconductorlayer. Thus, when separation is performed from the manufacturingsubstrate to a supporting substrate in a later process, separation at aninterface of the separation layer can be easily performed.

Further, the layer containing an oxide of tungsten may be formed byperforming thermal oxidation treatment, oxygen plasma treatment,treatment with a highly oxidizing solution such as ozone water, or thelike on the surface of the layer containing tungsten. The plasmatreatment and the heat treatment may be performed in an atmosphere ofoxygen, nitrogen, or dinitrogen monoxide alone, or a mixed gas of any ofthese gasses and another gas. The same applies to the case of forming alayer containing a nitride, an oxynitride, or a nitride oxide oftungsten. After a layer containing tungsten is formed, a silicon nitridelayer, a silicon oxynitride layer, or a silicon nitride oxide layer maybe formed thereover.

A layer 304 to be separated is formed over the separation layer 302. Thelayer 304 to be separated has the first insulating layer 8104 over whichthe thin film transistor 170, the thin film transistor 180, thecapacitor 147, the color filter layer 191, the overcoat layer 192, theoxide insulating film 107, the protective insulating layer 106, theprotective insulating layer 109, and the first electrode layer 110 ofthe light-emitting element are formed.

First, the first insulating layer 8104 is formed over the separationlayer 302. The first insulating layer 8104 is preferably formed as asingle-layer or a multilayer of an insulating film containing nitrogenand silicon, such as a silicon nitride film, a silicon oxynitride film,or a silicon nitride oxide film.

The first insulating layer 8104 can be formed using a sputtering method,a plasma CVD method, a coating method, a printing method, or the like.For example, the first insulating layer 8104 is formed at a filmformation temperature of 250° C. to 400° C. by a plasma CVD method,whereby a dense film having very low water permeability can be obtained.Note that the first insulating layer 8104 is preferably formed to athickness of 10 nm to 1000 nm, more preferably a thickness of 100 nm to700 nm.

By forming the first insulating layer 8104, separation can be easilyperformed at an interface between the first insulating layer 8104 andthe separation layer 302 in a later separation process. Further, thesemiconductor element or the wiring can be prevented from being crackedor damaged in the later separation process. Furthermore, the firstinsulating layer 8104 serves as a protective layer of the light-emittingdevice 8400.

The layer 304 to be separated is formed over the first insulating layer8104. The layer 304 to be separated can be formed using the methoddescribed in Embodiment 1; accordingly a detailed description thereof isomitted here.

Next, a second manufacturing substrate 306 is temporarily bonded to thelayer 304 to be separated using an adhesive layer 305 which can beremoved. By bonding the second manufacturing substrate 306 to the layer304 to be separated, the layer 304 to be separated can be easilyseparated from the separation layer 302. In addition, it is possible tolower stress added to the layer 304 to be separated through theseparation process, and the thin film transistors can be protected.Further, since the adhesive layer 305 which can be removed is used, thesecond manufacturing substrate 306 can be easily removed after use.

As the adhesive layer 305 which can be removed, for example, awater-soluble resin can be used. Unevenness of the layer 304 to beseparated is reduced by applying the water soluble-resin, so that thelayer 304 to be separated can be easily bonded to the secondmanufacturing substrate 306. In addition, as the adhesive layer 305which can be removed, a stack of water-soluble resin and an adhesivecapable of being separated by light or heat may be used.

Next, the layer 304 to be separated is separated from the firstmanufacturing substrate 300 (see FIG. 28B). As a separation method, anyof various methods can be used.

For example, when a metal oxide film is formed as the separation layer302 on the side that is in contact with the first insulating layer 8104,the metal oxide film is weakened by crystallization, so that the layer304 to be separated can be separated from the first manufacturingsubstrate 300. In addition, after the metal oxide film is weakened bycrystallization, a part of the separation layer 302 may be removed byetching using a solution or a fluoride halogen gas such as NF₃, BrF₃, orClF₃ and separation may be performed along the weakened metal oxidefilm.

When a film containing nitrogen, oxygen, hydrogen, or the like (e.g., anamorphous silicon film containing hydrogen, an alloy film containinghydrogen, or an alloy film containing oxygen) is used as the separationlayer 302 and a substrate having a light-transmitting property is usedas the first manufacturing substrate 300, the following manner can beused: the separation layer 302 is irradiated with laser light throughthe first manufacturing substrate 300, and nitrogen, oxygen, or hydrogencontained in the separation layer is evaporated, so that separation canoccur between the first manufacturing substrate 300 and the separationlayer 302.

Further, by removing the separation layer 302 by etching, the layer 304to be separated may be separated from the first manufacturing substrate300.

It is also possible to use a method for removing the first manufacturingsubstrate 300 by mechanical polishing, a method for removing the firstmanufacturing substrate 300 by etching using a halogen fluoride gas suchas NF₃, BrF₃ or ClF₃, or HF, or the like. In this case, the separationlayer 302 is not necessarily used.

Moreover, the layer 304 to be separated can be separated from the firstmanufacturing substrate 300 in the following manner: a groove to exposethe separation layer 302 is formed by laser irradiation, by etchingusing a gas, a solution, or the like, or with a sharp knife or ascalpel, so that separation occurs along the interface between theseparation layer 302 and the first insulating layer 8104 serving as aprotective layer, with the groove used as a trigger.

As the separation method, for example, mechanical force (separationtreatment with a human hand or with a gripper, separation treatment byrotation of a roller, or the like) may also be used. Alternatively, aliquid may be dropped into the groove to allow the liquid to beinfiltrated into the interface between the separation layer 302 and thefirst insulating layer 8104, which may be followed by the separation ofthe layer 304 to be separated from the separation layer 302. Furtheralternatively, a method may be used in which a fluoride gas such as NF₃,BrF₃, or ClF₃ is introduced into the groove and the separation layer 302is removed by etching with the use of the fluoride gas so that the layer304 to be separated is separated from the first manufacturing substrate300 having an insulating surface. Furthermore, the separation may beperformed while pouring a liquid such as water during the separation.

As another separation method, when the separation layer 302 is formedusing tungsten, separation can be performed while the separation layeris etched by a mixed solution of ammonia water and hydrogen peroxidewater.

Next, the first substrate 8100 which is thin, lightweight and has alight-transmitting property is bonded to the layer 304 to be separatedusing the resin layer 8141 (see FIG. 29A).

As the first substrate 8100 which is thin, lightweight and has alight-transmitting property, a substrate having flexibility and alight-transmitting property with respect to visible light can be used.For example, it is preferable to use a polyester resin such aspolyethylene terephthalate (PET) or polyethylene naphthalate (PEN), apolyacrylonitrile resin, a polyimide resin, a polymethyl methacrylateresin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, apolyamide resin, a cycloolefin resin, a polystyrene resin, a polyamideimide resin, or a polyvinylchloride resin, or the like. In addition,over the first substrate 8100, a protective film with low waterpermeability, such as a film containing nitrogen and silicon, e.g., asilicon nitride film or a silicon oxynitride film, or a film containingnitrogen and aluminum e.g., an aluminum nitride film, may be formed inadvance. Note that a structure body in which a fibrous body isimpregnated with an organic resin (so-called prepreg) may be used as thefirst substrate 8100.

In the case where a fibrous body is included in the material of thefirst substrate 8100, a high-strength fiber of an organic compound or aninorganic compound is used as the fibrous body. A high-strength fiber isspecifically a fiber with a high tensile modulus of elasticity or afiber with a high Young's modulus. As a typical example of ahigh-strength fiber, a polyvinyl alcohol based fiber, a polyester basedfiber, a polyamide based fiber, a polyethylene based fiber, an aramidbased fiber, a polyparaphenylene benzobisoxazole fiber, a glass fiber,or a carbon fiber can be given. As a glass fiber, there is a glass fiberusing E glass, S glass, D glass, Q glass, or the like. These fibers maybe used in a state of a woven fabric or a nonwoven fabric, and astructure body in which this fibrous body is impregnated with an organicresin and the organic resin is cured may be used as the first substrate8100. When the structure body including the fibrous body and the organicresin is used as the first substrate 8100, reliability against bendingor breaking due to local pressure can be increased, which is preferable.

Note that in the case where the first substrate 8100 includes the abovefibrous body, in order to reduce prevention of light emitted from thelight-emitting element to the outside, the fibrous body is preferably ananofiber with a diameter of 100 nm or less. Further, refractive indexesof the fibrous body and the organic resin or the adhesive preferablymatch with each other.

As the resin layer 8141, various curable adhesives, e.g., a lightcurable adhesive such as a UV curable adhesive, a reactive curableadhesive, a thermal curable adhesive, and an anaerobic adhesive can beused. As the material of these adhesives, an epoxy resin, an acrylicresin, a silicone resin, a phenol resin, or the like can be used.

Note that in the case where a prepreg is used as the first substrate8100, the layer 304 to be separated and the first substrate 8100 aredirectly bonded to each other by pressure bonding without using theadhesive. At this time, as the organic resin for the structure body, areactive curable resin, a thermal curable resin, a UV curable resin, orthe like which is better cured by additional treatment is preferablyused.

After forming the first substrate 8100, the second manufacturingsubstrate 306 and the adhesive layer 305 which can be removed areremoved, whereby the first electrode layer 110 is exposed (see FIG.29B).

According to the above process, the layer 304 to be separated whichincludes the thin film transistor 170, the thin film transistor 180, andthe first electrode layer 110 of the light-emitting element, can beformed over the first substrate 8100.

Next, the partition 193 covering a part of the first electrode layer 110is formed. The EL layer 194 is formed over the first electrode layer110. The EL layer 194 can be formed using either a low molecularmaterial or a high molecular material. Note that a material forming theEL layer 194 is not limited to a material containing only an organiccompound material, and it may partly contain an inorganic compoundmaterial. The EL layer 194 needs to have at least a light-emittinglayer, and a single-layer structure that is formed using a singlelight-emitting layer or a stacked-layer structure including layers eachhaving different functions may be used. For example, functional layerssuch as a hole-injection layer, a hole-transport layer, acarrier-blocking layer, an electron-transport layer, and anelectron-injection layer can be combined as appropriate in addition to alight-emitting layer. Note that a layer having two or more functions ofthe respective functions of the layers may be included.

The EL layer 194 can be formed using either a wet process or a dryprocess, such as an evaporation method, an inkjet method, a spin coatingmethod, a dip coating method, or a nozzle printing method.

Next, the second electrode layer 195 is formed over the EL layer 194.The second electrode layer 195 may be formed using a material similar tothat of the first electrode layer 110. Note that in the case where thefirst electrode layer 110 serves as an anode, the second electrode layer195 serves as a cathode and in the case where the first electrode layer110 serves as a cathode, the second electrode layer 195 serves as ananode; therefore, the first electrode layer 110 and the second electrodelayer 195 are formed by selecting a material having a work functioncorresponding to the polarity of the respective electrode layers.

In this embodiment, the first electrode layer 110 is used as an anode,and the EL layer 194 has a structure in which a hole-injection layer, ahole-transport layer, a light-emitting layer, and an electron-injectionlayer are sequentially stacked from the first electrode layer 110 side.Various kinds of materials can be used for the light-emitting layer. Forexample, a fluorescent compound which exhibits fluorescence or aphosphorescent compound which exhibits phosphorescence can be used. Inaddition, as the second electrode layer 195, a material with a low workfunction is used. Since light is emitted through the first electrodelayer 110 side, a highly reflective material is selected for the secondelectrode layer 195.

Through the above process, the pixel portion 8250 including the thinfilm transistor 170 and the light-emitting element is formed.

Further, a protective film may be formed over the second electrode layer195. For example, the protective film is formed as a single-layer or amultilayer using a material containing nitrogen and silicon such assilicon nitride, silicon nitride oxide, or silicon oxynitride; aluminumoxide; or the like by a sputtering method, a plasma CVD method, acoating method, a printing method, or the like. Alternatively, the aboveinorganic insulating film and an organic insulating film such as a resinfilm may be stacked to form the protective film. By forming theprotective film, moisture and gas such as oxygen can be prevented fromentering the element portion. The thickness of the protective filmfunctioning as a protective layer is preferably 10 nm to 1000 nm, morepreferably, 100 to 700 nm Note that the terminal portions 8254 and 8255are covered with a shadow mask or the like so that the protective filmis not formed thereover (see FIG. 30).

Next, the second substrate 8144 is bonded to cover the pixel portion8250 and the driving circuit portion 8252. The second substrate 8144 isbonded over the pixel portion 8250 and the driving circuit portion 8252using the resin layer 8142.

The resin layer 8142 is preferably formed using a material with goodadhesion properties. For example, the following materials can be used:an organic compound such as acrylic resins, polyimide resins, melamineresins, polyester resins, polycarbonate resins, phenol resins, epoxyresins, polyacetal, polyether, polyurethane, polyamide (nylon), furanresins, or diallylphthalate resins; inorganic siloxane polymersincluding a Si—O—Si bond among compounds including silicon, oxygen, andhydrogen, formed by using a siloxane-polymer-based material typified bysilica glass as a starting material; or organic siloxane polymers inwhich hydrogen bonded with silicon is substituted by an organic groupsuch as methyl or phenyl, typified by alkylsiloxane polymers,alkylsilsesquioxane polymers, silsesquioxane hydride polymers, oralkylsilsesquioxane hydride polymers. Further, a fibrous body may beincluded in these materials of the resin layer 8142.

The resin layer 8142 can be formed, for example, by applying acomposition using a coating method and then drying by heating.Alternatively, a structure body in which a fibrous body is impregnatedwith an organic resin may be used as the resin layer 8142.

As the second substrate 8144, a substrate which is thin and has lowwater permeability is used. For example, a metal substrate can be used.A material for forming the metal substrate is not limited to aparticular material; however, aluminum, copper, nickel, an alloy ofmetals such as an aluminum alloy or stainless steel, or the like can bepreferably used. Note that before bonding, the second substrate 8144 ispreferably subjected to baking or plasma treatment in vacuum so as toremove moisture attached to the surface of the metal substrate. A resinfilm may also be formed on the surface of the second substrate 8144 toprotect the second substrate 8144.

The second substrate 8144 can also be bonded using a laminator. Forexample, a sheet-like adhesive is applied to the metal substrate using alaminator and the metal substrate may further be bonded to the pixelportion 8250 and the driving circuit portion 8252 using a laminator.Alternatively, the resin layer 8142 is printed on the second substrate8144 by screen printing or the like and the second substrate 8144 isbonded to the light-emitting element using a laminator. Note that thisprocess is preferably carried out under a reduced pressure, so thatbubbles are hardly entered (see FIG. 27).

In the above-described manner, the light-emitting device, one embodimentof the present invention can be manufactured.

Note that this embodiment shows an example of the method in which thethin film transistor and the first electrode of the light-emittingelement and formed in a layer to be separated; however, the inventiondisclosed in this specification is not limited thereto. The separationand transfer may be performed after the light-emitting element is formed(i.e., after a second electrode of the light-emitting element isformed). Further, the layer to be separated including only the firstinsulating layer and the first electrode layer may be separated andtransferred to the first substrate, and the thin film transistor and thelight-emitting element may be manufactured after the transfer.Furthermore, only the first insulating layer may be formed over themanufacturing substrate, and then separated and transferred to asubstrate, and the thin film transistor and the light-emitting elementmay be manufactured thereafter.

The light-emitting device 8400 of this embodiment is formed between thefirst substrate 8100 which is thin, lightweight and has alight-transmitting property, and the second substrate 8144 which is thinand has low water permeability, so that a light-emitting device which islightweight, easily handled and has flexibility can be provided. Inaddition, as a support body of the light-emitting device, the secondsubstrate 8144 with low water permeability is formed using a metalsubstrate. As a result, moisture is prevented from entering thelight-emitting element, and a light-emitting device with a long lifetimecan be obtained.

According to this embodiment, a thin film transistor manufactured usinga substrate having high heat resistance can be transferred to a firstsubstrate which is thin, lightweight and has a light-transmittingproperty. Therefore, a thin film transistor with high reliability andexcellent electric characteristics can be formed without beingrestricted by the heat resistance of the first substrate. Alight-emitting device in which such a thin film transistor is formed ina pixel portion and a driving circuit portion formed on the samesubstrate has excellent reliability and operation characteristics.

Note that the structure described in this embodiment can be combinedwith any of the structures described in other embodiments asappropriate.

Embodiment 7

In this embodiment, in the light-emitting device described in any ofEmbodiments 1 to 6, an example of manufacturing an active matrixlight-emitting display device with the use of a thin film transistor anda light-emitting element utilizing electroluminescence will bedescribed.

Light-emitting elements utilizing electroluminescence are classifiedaccording to whether a light-emitting material is an organic compound oran inorganic compound. In general, the former is referred to as anorganic EL element, and the latter is referred to as an inorganic ELelement.

In the organic EL element, by application of voltage to a light-emittingelement, electrons and holes are separately injected from a pair ofelectrodes into a layer containing a light-emitting organic compound,and thus current flows. Then, the carriers (electrons and holes)recombine, so that the light-emitting organic compound is excited. Thelight-emitting organic compound returns to a ground state from theexcited state, thereby emitting light. Owing to such a mechanism, such alight-emitting element is referred to as a current-excitationlight-emitting element.

The inorganic EL elements are classified according to their elementstructures into a dispersion-type inorganic EL element and a thin-filminorganic EL element. The dispersion-type inorganic EL element has alight-emitting layer where particles of a light-emitting material aredispersed in a binder, and its light emission mechanism isdonor-acceptor recombination type light emission which utilizes a donorlevel and an acceptor level. The thin-film inorganic EL element has astructure where a light-emitting layer is sandwiched between dielectriclayers, which are further sandwiched between electrodes, and its lightemission mechanism is localized type light emission that utilizesinner-shell electron transition of metal ions. Note that an example ofan organic EL element as a light-emitting element is described here.

FIG. 19 shows an example of a pixel structure to which digital timegrayscale driving can be applied, as an example of a light-emittingdevice.

The structure and operation of a pixel to which digital time grayscaledriving can be applied are described. Here, the following example isshown: one pixel includes two n-channel transistors each of which usesan oxide semiconductor layer for a channel formation region.

A pixel 6400 includes a switching transistor 6401, a driving transistor6402, a light-emitting element 6404, and a capacitor 6403. A gate of theswitching transistor 6401 is connected to a scan line 6406, a firstelectrode (one of a source electrode and a drain electrode) of theswitching transistor 6401 is connected to a signal line 6405, and asecond electrode (the other of the source electrode and the drainelectrode) of the switching transistor 6401 is connected to a gate ofthe driving transistor 6402. The gate of the driving transistor 6402 isconnected to a power supply line 6407 through the capacitor 6403. Afirst electrode of the driving transistor 6402 is connected to the powersupply line 6407. A second electrode of the driving transistor 6402 isconnected to a first electrode (pixel electrode) of the light-emittingelement 6404. A second electrode of the light-emitting element 6404corresponds to a common electrode 6408. The common electrode 6408 iselectrically connected to a common potential line provided over the samesubstrate.

The second electrode (common electrode 6408) of the light-emittingelement 6404 is set to a low power supply potential. Note that the lowpower supply potential is a potential which satisfies the low powersupply potential<a high power supply potential with reference to thehigh power supply potential that is set to the power supply line 6407.As the low power supply potential, GND, 0 V, or the like may beemployed, for example. A potential difference between the high powersupply potential and the low power supply potential is applied to thelight-emitting element 6404 so that current flows through thelight-emitting element 6404, whereby the light-emitting element 6404emits light. Thus, each potential is set so that the potentialdifference between the high power supply potential and the low powersupply potential is higher than or equal to a forward threshold voltageof the light-emitting element 6404.

When gate capacitance of the driving transistor 6402 is used as asubstitute for the capacitor 6403, the capacitor 6403 can be omitted.The gate capacitance of the driving transistor 6402 may be formedbetween a channel region and a gate electrode.

In the case of a voltage-input voltage driving method, a video signal isinput to the gate of the driving transistor 6402 so that the drivingtransistor 6402 is completely turned on or off. That is, the drivingtransistor 6402 operates in a linear region; thus, voltage higher thanthe voltage of the power supply line 6407 is applied to the gate of thedriving transistor 6402. Note that voltage higher than or equal to(voltage of the power supply line+V_(th) of the driving transistor 6402)is applied to the signal line 6405.

In the case of performing analog grayscale driving instead of digitaltime grayscale driving, the same pixel structure as in FIG. 19 can beused by changing signal input.

In the case where the analog grayscale driving is performed, a voltagehigher than or equal to voltage which is the sum of the forward voltageof the light-emitting element 6404 and V_(th) of the driving transistor6402 is applied to the gate of the driving transistor 6402. The forwardvoltage of the light-emitting element 6404 refers to a voltage at whicha desired luminance is obtained, and includes at least forward thresholdvoltage. By inputting a video signal to enable the driving transistor6402 to operate in a saturation region, current can flow through thelight-emitting element 6404. In order that the driving transistor 6402can operate in the saturation region, the potential of the power supplyline 6407 is set higher than the gate potential of the drivingtransistor 6402. With an analog video signal, current in accordance withthe video signal flows through the light-emitting element 6404, and theanalog grayscale driving can be performed.

Note that the pixel structure shown in FIG. 19 is not limited thereto.For example, a switch, a resistor, a capacitor, a transistor, a logiccircuit, or the like may be added to the pixel shown in FIG. 19.

Next, structures of the light-emitting element are described withreference to FIGS. 20A to 20C. Here, a cross-sectional structure of apixel is described by taking an n-channel driving TFT as an example.Driving TFTs 7001, 7011, and 7021 used in light-emitting devices shownin FIGS. 20A, 20B, and 20C in Embodiments 1 to 5, respectively, can beformed in a manner similar to that of the thin film transistor describedin any of Embodiments 1 to 5, and are highly reliable thin filmtransistors each including an oxide semiconductor layer.

In order to extract light emitted from the light-emitting element, atleast one of an anode and a cathode is required to transmit light. Athin film transistor and a light-emitting element are formed over asubstrate. A light-emitting element can have a top emission structure inwhich light is extracted through the surface opposite to the substrate;a bottom emission structure in which light is extracted through thesurface on the substrate side; or a dual emission structure in whichlight is extracted through the surface opposite to the substrate and thesurface on the substrate side. The pixel structure can be applied to alight-emitting element having any of these emission structures.

A light-emitting element having the bottom emission structure will bedescribed with reference to FIG. 20A.

FIG. 20A is a cross-sectional view of a pixel in the case where thedriving TFT 7011 is an n-channel transistor and light is emitted from alight-emitting element 7012 to a first electrode layer 7013 side. InFIG. 20A, the first electrode layer 7013 of the light-emitting element7012 is formed over a light-transmitting conductive film 7017 which iselectrically connected to the driving TFT 7011. An EL layer 7014 and asecond electrode layer 7015 are stacked in this order over the firstelectrode layer 7013. Note that the conductive film 7017 is electricallyconnected to a drain electrode layer of the driving TFT 7011 through acontact hole formed in a protective insulating layer 7035, a protectiveinsulating layer 7032, and an oxide insulating layer 7031.

As the light-emitting conductive film 7017, the followinglight-transmitting conductive films can be used: film of indium oxideincluding tungsten oxide, indium zinc oxide including tungsten oxide,indium oxide including titanium oxide, indium tin oxide includingtitanium oxide, indium tin oxide, indium zinc oxide, or indium tin oxideto which silicon oxide is added.

Further, a variety of materials can be used for the first electrodelayer 7013 of the light-emitting element. For example, in the case wherethe first electrode layer 7013 is used as a cathode, a material having alow work function such as an alkali metal such as Li or Cs, an alkalineearth metal such as Mg, Ca, or Sr, an alloy containing any of them(e.g., Mg:Ag, Al:Li), or a rare earth metal such as Yb or Er ispreferable. In FIG. 20A, the first electrode layer 7013 is formed tohave a thickness through which light can be transmitted (preferably,approximately 5 nm to 30 nm). For example, an aluminum film with athickness of 20 nm is used as the first electrode layer 7013.

Alternatively, a light-transmitting conductive film and an aluminum filmmay be stacked and then selectively etched so as to form thelight-transmitting conductive film 7017 and the first electrode layer7013, which is preferable because the etching can be performed using thesame mask.

Further, the periphery portion of the first electrode layer 7013 iscovered with a partition 7019. The partition 7019 is formed using a filmof an organic resin such as polyimide, acrylic, polyamide, or epoxy, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition 7019 be formed using a photosensitiveresin material to have an opening portion over the first electrode layer7013 so that a sidewall of the opening portion is formed as a tiltedsurface with continuous curvature. When a photosensitive resin materialis used for the partition 7019, a step of forming a resist mask can beomitted.

Further, the EL layer 7014 formed over the first electrode layer 7013and the partition 7019 may include at least a light-emitting layer andbe formed using a single-layer or a plurality of layers stacked. Whenthe EL layer 7014 is formed using a plurality of layers, anelectron-injection layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injection layer are stacked inthis order over the first electrode layer 7013 functioning as a cathode.Note that it is not necessary to form all of these layers.

The stacking order is not limited to the above order. The firstelectrode layer 7013 may function as an anode and a hole-injectionlayer, hole-transport layer, a light-emitting layer, anelectron-transport layer, and an electron-injection layer may be stackedin this order over the first electrode layer 7013. Note that from apower consumption standpoint, it is preferable to make the firstelectrode layer 7013 function as a cathode and to stack anelectron-injection layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injection layer in this orderover the first electrode layer 7013 because increase in driving voltageof the driving circuit portion can be suppressed and thus powerconsumption can be reduced.

Further, a variety of materials can be used for the second electrodelayer 7015 formed over the EL layer 7014. For example, in the case wherethe second electrode layer 7015 is used as an anode, a material having ahigh work function, such as ZrN, Ti, W, Ni, Pt, or Cr, or a transparentconductive material such as ITO, IZO, or ZnO is preferable. Further,over the second electrode layer 7015, a light-blocking film 7016 isformed using a metal blocking light, a metal reflecting light, or thelike. In this embodiment, an ITO film is used as the second electrodelayer 7015 and a Ti film is used as the light-blocking film 7016.

The light-emitting element 7012 corresponds to a region where the ELlayer 7014 including a light-emitting layer is sandwiched with the firstelectrode layer 7013 and the second electrode layer 7015. In the case ofthe element structure shown in FIG. 20A, light is emitted from thelight-emitting element 7012 to the first electrode layer 7013 side topass through a color filter layer 7033 to the outside as indicated by anarrow.

The color filter layer 7033 is formed by a droplet discharge method suchas an ink-jet method, a printing method, an etching method with the useof a photolithography technique, or the like.

The color filter layer 7033 is covered with an overcoat layer 7034 andthe protective insulating layer 7035 is further formed thereover. Notethat although the overcoat layer 7034 is illustrated to have a smallthickness in FIG. 20A, the overcoat layer 7034 has a function ofreducing roughness caused by the color filter layer 7033.

Next, a light-emitting element having the dual emission structure willbe described with reference to FIG. 20B.

In FIG. 20B, a first electrode layer 7023 of a light-emitting element7022 is formed over a light-transmitting conductive film 7027 which iselectrically connected to the driving TFT 7021. An EL layer 7024 and asecond electrode layer 7025 are stacked in this order over the firstelectrode layer 7023. Note that the conductive film 7027 is electricallyconnected to a drain electrode layer of the driving TFT 7021 through acontact hole formed in a protective insulating layer 7045, a protectiveinsulating layer 7042, and an oxide insulating layer 7041.

As the light-emitting conductive film 7027, the followinglight-transmitting conductive film can be used: film of indium oxideincluding tungsten oxide, indium zinc oxide including tungsten oxide,indium oxide including titanium oxide, indium tin oxide includingtitanium oxide, indium tin oxide, indium zinc oxide, or indium tin oxideto which silicon oxide is added.

A variety of materials can be used for the first electrode layer 7023.For example, in the case where the first electrode layer 7023 is used asa cathode, a material having a low work function such as an alkali metalsuch as Li or Cs, an alkaline earth metal such as Mg, Ca, or Sr, analloy containing any of them (e.g., Mg:Ag, Al:Li), or a rare earth metalsuch as Yb or Er is preferable. In this embodiment, the first electrodelayer 7023 functions as a cathode and is formed to have a thicknessthrough which light can be transmitted (preferably, approximately 5 nmto 30 nm). For example, an aluminum film with a thickness of 20 nm isused as the cathode.

Alternatively, a light-transmitting conductive film and an aluminum filmmay be stacked and then selectively etched so as to form thelight-transmitting conductive film 7027 and the first electrode layer7023. In this case, it is preferable that the etching can be performedusing the same mask.

Further, the periphery portion of the first electrode layer 7023 iscovered with a partition 7029. The partition 7029 is formed using a filmof an organic resin such as polyimide, acrylic, polyamide, or epoxy, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition 7029 be formed using a photosensitiveresin material to have an opening portion over the first electrode layer7023 so that a sidewall of the opening portion is formed as a tiltedsurface with continuous curvature. When a photosensitive resin materialis used for the partition 7029, a step of forming a resist mask can beomitted.

Further, the EL layer 7024 formed over the first electrode layer 7023and the partition 7029 may include at least a light-emitting layer andbe formed using a single-layer or a plurality of layers stacked. Whenthe EL layer 7024 is formed using a plurality of layers, anelectron-injection layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injection layer are stacked inthis order over the first electrode layer 7023 functioning as a cathode.Note that it is not necessary to form all of these layers.

The stacking order is not limited to the above order. The firstelectrode layer 7023 may function as an anode and a hole-injectionlayer, hole-transport layer, a light-emitting layer, anelectron-transport layer, and an electron-injection layer may be stackedin this order over the anode. Note that from a power consumptionstandpoint, it is preferable to make the first electrode layer 7023function as a cathode and to stack an electron-injection layer, anelectron-transport layer, a light-emitting layer, a hole-transportlayer, and a hole-injection layer in this order over the cathode becausepower consumption can be reduced.

Further, a variety of materials can be used for the second electrodelayer 7025 formed over the EL layer 7024. For example, in the case wherethe second electrode layer 7025 is used as an anode, a material having ahigh work function, for example, a transparent conductive material suchas ITO, IZO, or ZnO, is preferably used. In this embodiment, the secondelectrode layer 7025 is used as an anode and an ITO film includingsilicon oxide is formed.

The light-emitting element 7022 corresponds to a region where the ELlayer 7024 including a light-emitting layer is sandwiched with the firstelectrode layer 7023 and the second electrode layer 7025. In the case ofthe element structure shown in FIG. 20B, light is emitted from thelight-emitting element 7022 to both the second electrode layer 7025 sideand the first electrode layer 7023 side as indicated by arrows.

A color filter layer 7043 is formed by a droplet discharge method suchas an ink-jet method, a printing method, an etching method with the useof a photolithography technique, or the like.

In addition, the color filter layer 7043 is covered with an overcoatlayer 7044 and the protective insulating layer 7045 is further formedthereover.

Note that when a light-emitting element having a dual emission structureis used and full color display is performed on both display surfaces,light from the second electrode layer 7025 side does not pass throughthe color filter layer 7043; therefore, a sealing substrate providedwith another color filter layer is preferably formed over the secondelectrode layer 7025.

Next, a light-emitting element having a top emission structure will bedescribed with reference to FIG. 20C.

FIG. 20C is a cross-sectional view of a pixel in the case where thedriving TFT 7001 is an n-channel transistor and light is emitted from alight-emitting element 7002 to a second electrode layer 7005 side. InFIG. 20C, a first electrode layer 7003 of the light-emitting element7002, which is electrically connected to the driving TFT 7001, isformed. An EL layer 7004 and the second electrode layer 7005 are stakedin this order over the first electrode layer 7003.

Further, a variety of materials can be used for the first electrodelayer 7003. For example, in the case where the first electrode layer7003 is used as a cathode, a material having a low work function such asan alkali metal such as Li or Cs, an alkaline earth metal such as Mg,Ca, or Sr, an alloy containing any of them (e.g., Mg:Ag, Al:Li), or arare earth metal such as Yb or Er is preferable.

Further, the periphery portion of the first electrode layer 7003 iscovered with a partition 7009. The partition 7009 is formed using a filmof an organic resin such as polyimide, acrylic, polyamide, or epoxy, aninorganic insulating film, or organic polysiloxane. It is particularlypreferable that the partition 7009 be formed using a photosensitiveresin material to have an opening portion over the first electrode layer7003 so that a sidewall of the opening portion is formed as a tiltedsurface with continuous curvature. When a photosensitive resin materialis used for the partition 7009, a step of forming a resist mask can beomitted.

Further, the EL layer 7004 formed over the first electrode layer 7003and the partition 7009 may include at least a light-emitting layer andbe formed using a single-layer or a plurality of layers stacked. Whenthe EL layer 7004 is formed using a plurality of layers, anelectron-injection layer, an electron-transport layer, a light-emittinglayer, a hole-transport layer, and a hole-injection layer are stacked inthis order over the first electrode layer 7003 used as a cathode. Notethat it is not necessary to form all of these layers.

The stacking order is not limited to the above order. A hole-injectionlayer, hole-transport layer, a light-emitting layer, anelectron-transport layer, and an electron-injection layer may be stackedin this order over the first electrode layer 7003 used as an anode.

In FIG. 20C, a hole-injection layer, a hole-transport layer, alight-emitting layer, an electron-transport layer, and anelectron-injection layer are stacked in this order over a stacked filmin which a Ti film, an aluminum film, and a Ti film are formed in thisorder, and thereover, a stacked-layer of a Mg:Ag alloy thin film and anITO film is formed.

Note that when the TFT 7001 is an n-type transistor, it is preferable tostack an electron-injection layer, an electron-transport layer, alight-emitting layer, a hole-transport layer, and a hole-injection layerin this order over the first electrode layer 7003 because increase involtage of the driving circuit can be suppressed and thus powerconsumption can be reduced.

As the light-transmitting second electrode layer 7005, the followinglight-transmitting conductive film can be used: film of indium oxideincluding tungsten oxide, indium zinc oxide including tungsten oxide,indium oxide including titanium oxide, indium tin oxide includingtitanium oxide, indium tin oxide, indium zinc oxide, or indium tin oxideto which silicon oxide is added.

The light-emitting element 7002 corresponds to a region where the ELlayer 7004 including a light-emitting layer is sandwiched with the firstelectrode layer 7003 and the second electrode layer 7005. In the case ofthe pixel shown in FIG. 20C, light is emitted from the light-emittingelement 7002 to the second electrode layer 7005 side as indicated by anarrow.

Further, in FIG. 20C, a drain electrode layer of the TFT 7001 iselectrically connected to the first electrode layer 7003 through acontact hole formed in an oxide insulating layer 7051, a protectiveinsulating layer 7052, and a protective insulating layer 7055. Aplanarizing insulating layer 7053 can be formed using a resin materialsuch as polyimide, acrylic, benzocyclobutene, polyamide, or epoxy. Inaddition to such resin materials, it is also possible to use a lowdielectric constant material (a low-k material), a siloxane-based resin,PSG (phosphosilicate glass), BPSG (borophosphosilicate glass), or thelike. Note that the planarizing insulating layer 7053 may be formed bystacking a plurality of insulating films formed using these materials.There is no particular limitation on a method for forming theplanarizing insulating layer 7053. The planarizing insulating layer 7053can be formed, depending on the material, with a method such as asputtering method, an SOG method, a spin coating method, a dippingmethod, a spray coating method, or a droplet discharge method (e.g., anink-jet method, screen printing, or offset printing), or with a meanssuch as a doctor knife, a roll coater, a curtain coater, or a knifecoater.

Further, the partition 7009 is formed to insulate the first electrodelayer 7003 from the first electrode layer 7003 of an adjacent pixel. Thepartition 7009 is formed using a film of an organic resin such aspolyimide, acrylic, polyamide, or epoxy, an inorganic insulating film,or organic polysiloxane. It is particularly preferable that thepartition 7009 be formed using a photosensitive resin material to havean opening portion over the first electrode layer 7003 so that asidewall of the opening portion is formed as a tilted surface withcontinuous curvature. When a photosensitive resin material is used forthe partition 7009, a step of forming a resist mask can be omitted.

In the structure in FIG. 20C, when full color display is performed, forexample, the light-emitting element 7002 is used as a greenlight-emitting element, one of the adjacent light-emitting elements isused as a red light-emitting element, and the other is used as a bluelight-emitting element. Alternatively, a light-emitting display devicecapable of full color display may be manufactured using four kinds oflight-emitting elements, which include a white light-emitting element aswell as the three kinds of the light-emitting elements.

Alternatively, in the structure in FIG. 20C, a light-emitting displaydevice capable of full color display may be manufactured in such amanner that all of the plurality of light-emitting elements which arearranged are white light-emitting elements and a sealing substratehaving a color filter or the like is arranged over the light-emittingelement 7002. When a material which exhibits a single color such aswhite is formed and then combined with a color filter or a colorconversion layer, full color display can be performed.

The examples in which the first electrode layer is in direct contactwith the thin film transistor are shown in FIGS. 20A to 20C; however, asdescribed in Embodiment 4, the drain electrode layer of the thin filmtransistor may be electrically connected to the first electrode layerthrough the connection electrode layer. The thin film transistorsdescribed in any of Embodiments 2, 3, and 5 may be used as the TFTs7001, 7011, and 7021.

Needless to say, display of monochromatic light emission can also beperformed. For example, a lighting device may be formed with the use ofwhite light emission; alternatively, an area-color type light-emittingdevice may be formed with the use of monochromatic light emission.

If necessary, an optical film such as a polarizing film including acircularly polarizing plate may be provided.

Note that, although the organic EL element is described here as thelight-emitting element, an inorganic EL element can also be provided asa light-emitting element.

Note that the example is described in which the thin film transistor(the driving TFT) which controls the driving of a light-emitting elementis electrically connected to the light-emitting element; however, astructure may be employed in which a TFT for current control isconnected between a driving TFT and a light-emitting element.

This embodiment can be combined with any of the other embodiments asappropriate.

Embodiment 8

In this embodiment, an example of an element structure of thelight-emitting element described in any of Embodiments 1 to 7 will bedescribed.

In the element structure shown in FIG. 21A, an EL layer 1003 including alight-emitting region is sandwiched between a pair of electrodes (afirst electrode 1001 and a second electrode 1002). Note that the firstelectrode 1001 is used as an anode and the second electrode 1002 is usedas a cathode as an example in the following description of thisembodiment.

The EL layer 1003 includes at least a light-emitting layer and may havea stacked structure including a functional layer in addition to thelight-emitting layer. As the functional layer other than thelight-emitting layer, a layer containing the following substances can beused: substance having a high hole-injection property, a substancehaving a high hole-transport property, a substance having a highelectron-transport property, a substance having a highelectron-injection property, a bipolar substance (a substance havinghigh electron-transport and hole-transport properties), or the like.Specifically, functional layers such as a hole-injection layer, ahole-transport layer, an electron-transport layer, and anelectron-injection layer can be used in combination as appropriate.

The light-emitting element shown in FIG. 21A emits light when currentflows because of a potential difference generated between the firstelectrode 1001 and the second electrode 1002, and holes and electronsare recombined in the EL layer 1003. That is, a light-emitting region isformed in the EL layer 1003.

Light emission is extracted outside through one of or both the firstelectrode 1001 and the second electrode 1002. Therefore, either or bothof the first electrode 1001 and the second electrode 1002 are formedusing a light-transmitting substance.

Note that a plurality of EL layers may be stacked between the firstelectrode 1001 and the second electrode 1002 as shown in FIG. 21B. Inthe case where n (n is a natural number of 2 or more) layers arestacked, a charge generation layer 1004 is preferably provided betweeneach m-th (m is a natural number of 1 to n−1) EL layer and each (m+1)-thEL layer.

The charge generation layer 1004 can be formed using a compositematerial of an organic compound and a metal oxide, a metal oxide, or acomposite material of an organic compound and an alkali metal, analkaline earth metal, or a compound thereof. Alternatively, thesematerials can be combined as appropriate. The composite material of anorganic compound and a metal oxide includes, for example, an organiccompound and a metal oxide such as V₂O₅, MoO₃, or WO₃. As the organiccompound, various compounds such as an aromatic amine compound, acarbazole derivative, aromatic hydrocarbon, and a high molecularcompound (oligomer, dendrimer, polymer, or the like) can be used. As theorganic compound, it is preferable to use the organic compound which hasa hole-transport property and has a hole mobility of 10⁻⁶ cm²/Vs orhigher. However, substances other than the above-described materials mayalso be used as long as the substances have higher hole-transportproperties than electron-transport properties. These materials used forthe charge generation layer 1004 are excellent in carrier-injectionproperty and carrier-transport property, and thus, a light-emittingelement can be driven with low current.

Note that the charge generation layer 1004 may be formed in acombination of a composite material of an organic compound and metaloxide with another material. For example, a layer containing a compositematerial of the organic compound and the metal oxide may be combinedwith a layer containing a compound of a substance selected fromsubstances having an electron-donating property and a compound having ahigh electron-transport property. Moreover, a layer containing acomposite material of the organic compound and the metal oxide may becombined with a transparent conductive film.

As for a light-emitting element having such a structure, problems suchas energy transfer and quenching are unlikely to occur, and alight-emitting element which has both high light emission efficiency andlong lifetime can be easily obtained due to expansion in the choice ofmaterials. In addition, a light-emitting element which providesphosphorescence from one of the EL layers and fluorescence from theother of the EL layers can be readily obtained.

Note that the charge generation layer 1004 has a function of injectingholes to one EL layer 1003 which is formed in contact with the chargegeneration layer 1004 and a function of injecting electrons to the otherEL layer 1003 which is formed in contact with the charge generationlayer 1004, when voltage is applied to the first electrode 1001 and thesecond electrode 1002.

The light-emitting element shown in FIG. 21B can provide a variety ofemission colors by changing the type of the light-emitting substancethat is used for the light-emitting layer. In addition, a plurality oflight-emitting substances of different emission colors are used as thelight-emitting substance, whereby light emission having a broad spectrumor white light emission can also be obtained.

In the case of obtaining white color light using the light-emittingelement shown in FIG. 21B, as for the combination of a plurality oflight-emitting layers, a structure for emitting white light includingred light, blue light, and green light may be used. For example, thestructure may include a first EL layer containing a blue fluorescentsubstance as a light-emitting substance and a second EL layer containinggreen and red phosphorescent substances as light-emitting substances.Alternatively, the structure may include a first EL layer exhibiting redlight emission, a second EL layer exhibiting green light emission, and athird EL layer exhibiting blue light emission. Further alternatively,with a structure including light-emitting layers emitting light ofcomplementary colors, white light emission can be obtained. When lightemission from the first EL layer and light emission from the second ELlayer have complementary colors to each other in an element includingtwo EL layers stacked, the combination of colors are as follows: blueand yellow, blue-green and red, and the like.

Note that in the structure of the above-described stacked element, byproviding the charge generation layer between the stacked EL layers, theelement can have long lifetime in a high luminance region while keepingthe current density low. In addition, the voltage drop due to resistanceof the electrode material can be reduced, whereby uniform light emissionin a large area is possible.

This embodiment can be implemented in appropriate combination with anyof the structures described in Embodiments 1 to 7.

Embodiment 9

In this embodiment, the appearance and a cross section of alight-emitting display panel (also referred to as a light-emittingpanel) will be described with reference to FIGS. 22A and 22B. FIG. 22Ais a plan view of a panel in which a thin film transistor and alight-emitting element which are formed over a first flexible substrateare sealed between the first flexible substrate and a second flexiblesubstrate with a sealant. FIG. 22B is a cross-sectional view taken alongline H-I in FIG. 22A.

A sealant 4505 is provided so as to surround a pixel portion 4502,signal line driving circuits 4503 a and 4503 b, and scan line drivingcircuits 4504 a and 4504 b which are provided over a first flexiblesubstrate 4501. In addition, a second flexible substrate 4506 isprovided over the pixel portion 4502, the signal line driving circuits4503 a and 4503 b, and the scan line driving circuits 4504 a and 4504 b.Accordingly, the pixel portion 4502, the signal line driving circuits4503 a and 4503 b, and the scan line driving circuits 4504 a and 4504 bare sealed together with a filler 4507, by the first flexible substrate4501, the sealant 4505, and the second flexible substrate 4506. It ispreferable that a panel be packaged (sealed) with a protective film(such as a bonding film or an ultraviolet curable resin film) or a covermaterial with high air-tightness and little degasification so that thepanel is not exposed to the outside air.

The pixel portion 4502, the signal line driving circuits 4503 a and 4503b, and the scan line driving circuits 4504 a and 4504 b formed over thefirst flexible substrate 4501 each include a plurality of thin filmtransistors. A thin film transistor 4510 included in the pixel portion4502 and a thin film transistor 4509 included in the signal line drivingcircuit 4503 a are shown as an example in FIG. 22B.

Any of the highly reliable thin film transistors including the oxidesemiconductor layers, which are described in Embodiments 1 to 5, can beused as the thin film transistors 4509 and 4510. As the thin filmtransistor 4509 for the driving circuit, any of the thin filmtransistors 180, 181, and 182 which are described in Embodiments 1 to 5can be used. As the thin film transistor 4510 for the pixel, any of thethin film transistors 170, 171, and 172 which are described inEmbodiments 1 to 5 can be used. In this embodiment, the thin filmtransistors 4509 and 4510 are n-channel thin film transistors.

A conductive layer 4540 is provided over an insulating layer 4544 so asto overlap with a channel formation region in an oxide semiconductorlayer of the thin film transistor 4509 for the driving circuit. Byforming the conductive layer 4540 so as to overlap with the channelformation region of the oxide semiconductor layer, the amount of changein the threshold voltage of the thin film transistor 4509 before andafter BT test can be reduced. Further, a potential of the conductivelayer 4540 may be the same as or different from that of the gateelectrode layer of the thin film transistor 4509. The conductive layer4540 can function also as a second gate electrode layer. Furthermore,the potential of the conductive layer 4540 may be GND or 0 V, or theconductive layer 4540 may be in a floating state.

Although not illustrated, a protective insulating layer such as theprotective insulating layer 106 shown in Embodiment 1 may be providedbetween an oxide insulating layer 4542 and the insulating layer 4544.

The thin film transistor 4510 is electrically connected to a firstelectrode layer 4517.

The oxide insulating layer 4542 may be formed using a material andmethod similar to those of the oxide insulating film 107 shown inEmbodiment 1.

A color filter layer 4545 is formed over the oxide insulating layer 4542so as to overlap with a light-emitting region of a light-emittingelement 4511.

In addition, in order to reduce the surface roughness of the colorfilter layer 4545, the color filter layer 4545 is covered with anovercoat layer 4543 functioning as a planarizing insulating film.

Further, an insulating layer 4544 is formed over the overcoat layer4543. The insulating layer 4544 may be formed using a material andsimilar to those of the protective insulating layer 109 shown inEmbodiment 1.

Reference numeral 4511 denotes a light-emitting element. The firstelectrode layer 4517 which is a pixel electrode included in thelight-emitting element 4511 is electrically connected to a source ordrain electrode layer of the thin film transistor 4510. Note thatalthough the light-emitting element 4511 has a stacked structure of thefirst electrode layer 4517, an electroluminescent layer 4512, and asecond electrode layer 4513, the structure of the light-emitting element4511 is not limited to the structure described in this embodiment. Thestructure of the light-emitting element 4511 can be changed asappropriate depending on the direction in which light is extracted fromthe light-emitting element 4511, or the like.

A partition 4520 is formed using an organic resin film, an inorganicinsulating film, or organic polysiloxane. It is particularly preferablethat the partition 4520 be formed using a photosensitive material and anopening be formed over the first electrode layer 4517 so that a sidewallof the opening is formed as a tilted surface with continuous curvature.

The electroluminescent layer 4512 may be formed with a single-layer or aplurality of layers stacked.

A protective film may be formed over the second electrode layer 4513 andthe partition 4520 in order to prevent entry of oxygen, hydrogen,moisture, carbon dioxide, or the like into the light-emitting element4511. As the protective film, a silicon nitride film, a silicon nitrideoxide film, a DLC film, or the like can be formed.

In addition, a variety of signals and potentials are supplied to thesignal line driving circuits 4503 a and 4503 b, the scan line drivingcircuits 4504 a and 4504 b, or the pixel portion 4502 from FPCs 4518 aand 4518 b.

A connection terminal electrode 4515 is formed from the same conductivefilm as the first electrode layer 4517 included in the light-emittingelement 4511, and a terminal electrode 4516 is formed from the sameconductive film as the source and drain electrode layers included in thethin film transistor 4509.

The connection terminal electrode 4515 is electrically connected to aterminal included in the FPC 4518 a through an anisotropic conductivefilm 4519.

The second flexible substrate located in the direction in which light isextracted from the light-emitting element 4511 needs to have alight-transmitting property. In that case, a light-transmitting materialsuch as a plastic plate, a polyester film, or an acrylic film is usedfor the second flexible substrate.

Further, as the filler 4507, an ultraviolet curable resin or athermosetting resin can be used, in addition to an inert gas such asnitrogen or argon. For example, PVC (polyvinyl chloride), acrylic,polyimide, an epoxy resin, a silicone resin, PVB (polyvinyl butyral), orEVA (ethylene vinyl acetate) can be used. For example, nitrogen is usedfor the filler.

Furthermore, if needed, an optical film such as a polarizing plate, acircularly polarizing plate (including an elliptically polarizingplate), a retardation plate (a quarter-wave plate or a half-wave plate),or a color filter may be provided as appropriate on a light-emittingsurface of the light-emitting element. Further, the polarizing plate orthe circularly polarizing plate may be provided with an anti-reflectionfilm. For example, anti-glare treatment may be performed by whichreflected light can be diffused by surface roughness so that the glarecan be reduced.

The signal line driving circuits 4503 a and 4503 b and the scan linedriving circuits 4504 a and 4504 b may be mounted as driving circuitsformed using a single crystal semiconductor film or a polycrystallinesemiconductor film over a flexible substrate separately prepared.Alternatively, only the signal line driving circuits or part thereof, orthe scan line driving circuits or part thereof may be separately formedand mounted. This embodiment is not limited to the structure shown inFIGS. 22A and 22B.

Through the above steps, a highly reliable light-emitting device(display panel) as a semiconductor device can be manufactured.

Embodiment 10

In this embodiment, an example is described below in which at least someof driving circuits and a thin film transistor provided in a pixelportion are formed over one flexible substrate.

The thin film transistor provided in the pixel portion is formed inaccordance with Embodiments 1 to 5. The thin film transistors describedin Embodiments 1 to 5 are n-channel TFTs; therefore, some of drivingcircuits which can be formed using n-channel TFTs are formed over oneflexible substrate as the thin film transistor of the pixel portion.

FIG. 12A shows an example of a block diagram of an active matrix displaydevice. The display device includes a pixel portion 5301, a first scanline driving circuit 5302, a second scan line driving circuit 5303, anda signal line driving circuit 5304 over a flexible substrate 5300. Inthe pixel portion 5301, a plurality of signal lines which are extendedfrom the signal line driving circuit 5304 and a plurality of scan lineswhich are extended from the first scan line driving circuit 5302 and thesecond scan line driving circuit 5303 are arranged. Note that pixelswhich include display elements are arranged in matrix in regions wherethe scan lines and the signal lines are crossed. In addition, theflexible substrate 5300 of the display device is connected to a timingcontrol circuit 5305 (also referred to as a controller or a control IC)through a connection portion such as a flexible printed circuit (FPC).

In FIG. 12A, the first scan line driving circuit 5302, the second scanline driving circuit 5303, and the signal line driving circuit 5304 areformed over one flexible substrate 5300 as the pixel portion 5301.Therefore, the number of components of a driving circuit which isprovided outside and the like is reduced, which leads to cost reduction.Further, if the driving circuit is provided outside the flexiblesubstrate 5300, wirings would need to be extended and the number ofconnections of wirings would be increased, but by providing the drivingcircuit over the flexible substrate 5300, the number of connections ofthe wirings can be reduced. Accordingly, improvement in reliability andyield can be achieved.

Note that the timing control circuit 5305 supplies, for example, a firstscan line driving circuit start signal (GSP1) and a scan line drivingcircuit clock signal (GCK1) to the first scan line driving circuit 5302.The timing control circuit 5305 supplies, for example, a second scanline driving circuit start signal (GSP2, also referred to as a startpulse) and a scan line driving circuit clock signal (GCK2) to the secondscan line driving circuit 5303. The timing control circuit 5305 suppliesa signal line driving circuit start signal (SSP), a signal line drivingcircuit clock signal (SCLK), video signal data (DATA, also simplyreferred to as a video signal), and a latch signal (LAT) to the signalline driving circuit 5304. Note that each clock signal may be aplurality of clock signals whose phases are shifted or may be suppliedtogether with an inverted clock signal (CKB) obtained by inverting theclock signal. Note that one of the first scan line driving circuit 5302and the second scan line driving circuit 5303 can be eliminated.

FIG. 12B shows a structure in which circuits with low driving frequency(e.g., the first scan line driving circuit 5302 and the second scan linedriving circuit 5303) are formed over the same flexible substrate 5300as the pixel portion 5301 and the signal line driving circuit 5304 isformed over a substrate which is different from the pixel portion 5301.With this structure, a driving circuit formed over the flexiblesubstrate 5300 can be formed using a thin film transistor with lowerfield effect mobility as compared to that of a transistor formed using asingle crystal semiconductor. Thus, increase in size of the displaydevice, reduction in cost, improvement in yield, or the like can beachieved.

In addition, the thin film transistors described in Embodiments 1 to 5are n-channel TFTs. FIGS. 13A and 13B show an example of a structure andoperation of a signal line driving circuit which is formed usingn-channel TFTs.

The signal line driving circuit includes a shift register 5601 and aswitching circuit 5602. The switching circuit 5602 includes a pluralityof switching circuits 5602_1 to 5602_N(N is a natural number). Theswitching circuits 5602_1 to 5602_N each include a plurality of thinfilm transistors 5603_1 to 5603_k (k is a natural number). An examplewhere the thin film transistors 5603_1 to 5603_k are n-channel TFTs isdescribed.

A connection relation in the signal line driving circuit is describedtaking the switching circuit 5602_1 as an example. First terminals ofthe thin film transistors 5603_1 to 5603_k are connected to wirings5604_1 to 5604_k, respectively. Second terminals of the thin filmtransistors 5603_1 to 5603_k are connected to signal lines S1 to Sk,respectively. Gates of the thin film transistors 5603_1 to 5603_k areconnected to a wiring 5605_1.

The shift register 5601 has a function of sequentially outputtingH-level signals (also referred to as H signals or signals at high powersupply potential level) to the wirings 5605_1 to 5605_N and sequentiallyselecting the switching circuits 5602_1 to 5602_N.

The switching circuit 5602_1 has a function of controlling a conductingstate between the wirings 5604_1 to 5604_k and the signal lines S1 to Sk(electrical continuity between the first terminals and the secondterminals), that is, a function of controlling whether potentials of thewirings 5604_1 to 5604_k are supplied to the signal lines S1 to Sk. Inthis manner, the switching circuit 5602_1 functions as a selector.Further, the thin film transistors 5603_1 to 5603_k each have functionsof controlling conduction states between the wirings 5604_1 to 5604_kand the signal lines S1 to Sk, that is, functions of supplying thepotentials of the wirings 5604_1 to 5604_k to the signal lines S1 to Sk.In this manner, each of the thin film transistors 5603_1 to 5603_kfunctions as a switch.

Note that video signal data (DATA) is input to each of the wirings5604_1 to 5604_k. The video signal data (DATA) is an analog signalcorresponding to an image data or image signal in many cases.

Next, operation of the signal line driving circuit in FIG. 13A isdescribed with reference to a timing chart in FIG. 13B. FIG. 13B showsexamples of signals Sout_1 to Sout_N and signals Vdata_1 to Vdata_k. Thesignals Sout_1 to Sout_N are examples of output signals from the shiftregister 5601. The signals Vdata_1 to Vdata_k are examples of signalsinput to the wirings 5604_1 to 5604_k. Note that one operation period ofthe signal line driving circuit corresponds to one gate selection periodin a display device. For example, one gate selection period is dividedinto periods T1 to TN. Each of the periods T1 to TN is a period duringwhich the video signal data (DATA) is written to pixels in a selectedrow.

Note that as for structures shown in drawings and the like of thisembodiment, distortion in signal waveforms and the like are exaggeratedfor simplicity in some cases. Thus, the scale is not necessarily limitedto that illustrated.

In the periods T1 to TN, the shift register 5601 sequentially outputsH-level signals to the wirings 5605_1 to 5605_N. For example, in theperiod T1, the shift register 5601 outputs the H-level signal to thewiring 5605_1. Then, the thin film transistors 5603_1 to 5603_k areturned on, so that the wirings 5604_1 to 5604_k and the signal lines S1to Sk are brought into conducting state. In this case, Data (S1) to Data(Sk) are input to the wirings 5604_1 to 5604_k, respectively. The Data(S1) to Data (Sk) are written to pixels in a selected row in first tok-th columns through the thin film transistors 5603_1 to 5603_k,respectively. Thus, in the periods T1 to TN, video signal data (DATA) issequentially written to the pixels in the selected row by k columns.

By writing video signal data (DATA) to pixels by a plurality of columnsas described above, the number of video signal data (DATA) or the numberof wirings can be reduced. Accordingly, the number of connections to anexternal circuit can be reduced. In addition, by writing video signalsto pixels by a plurality of columns, writing time can be extended andinsufficient writing of video signals can be prevented.

Note that as the shift register 5601 and the switching circuit 5602, acircuit including the thin film transistor described in any ofEmbodiments 1 to 5 can be used. In that case, the shift register 5601can be constituted by only n-channel transistors or only p-channeltransistors.

The structure of a scan line driving circuit will be described. The scanline driving circuit includes a shift register. The scan line drivingcircuit may also include a level shifter, a buffer, or the like in somecases. In the scan line driving circuit, a clock signal (CLK) and astart pulse signal (SP) are input to the shift register, whereby aselection signal is generated. The generated selection signal isbuffered and amplified in the buffer, and the resulting signal issupplied to a corresponding scan line. Gate electrodes of transistors inpixels of one line are connected to a scan line. Since the transistorsin the pixels of one line must be turned on all at once, a buffer whichcan supply a large amount of current is used.

One embodiment of a shift register which is used for a part of the scanline driving circuit and/or the signal line driving circuit is describedwith reference to FIGS. 14A to 14D and FIGS. 15A and 15B.

A shift register of a scan line driving circuit and/or a signal linedriving circuit is described with reference to FIGS. 14A to 14D andFIGS. 15A and 15B. The shift register includes first to N-th pulseoutput circuits 10_1 to 10_N(N is a natural number of 3 or more) (seeFIG. 14A). A first clock signal CK1 from a first wiring 11, a secondclock signal CK2 from a second wiring 12, a third clock signal CK3 froma third wiring 13, and a fourth clock signal CK4 from a fourth wiring 14are supplied in the first to N-th pulse output circuits 10_1 to 10_N ofthe shift register shown in FIG. 14A. In addition, a start pulse SP1 (afirst start pulse) from a fifth wiring 15 is input to the first pulseoutput circuit 10_1. Further, a signal from the pulse output circuit10_(n−1) of the previous stage (referred to as a previous stage signalOUT (n−1)) is input to the n-th pulse output circuit 10_n (n is anatural number of 2 or more and Nor less) in a second or subsequentstage. A signal from the third pulse output circuit 10_3 which is twostages after the first pulse output circuit 10_1 is input to the firstpulse output circuit 10_1. Similarly, a signal from the (n+2)-th pulseoutput circuit 10_(n+2) which is two stages after the n-th pulse outputcircuit 10_n (referred to as a subsequent stage signal OUT (n+2)) isinput to the n-th pulse output circuit 10_n in the second or subsequentstage. Therefore, the pulse output circuits in respective stages outputfirst output signals (OUT (1) (SR) to OUT (N) (SR)) which is input tothe pulse output circuit in the subsequent stage and/or the pulse outputcircuit of the stage before the preceding stage. Furthermore, the pulseoutput circuits in respective stages output second output signals (OUT(1) to OUT (N)) which are electrically connected to another wiring orthe like. Note that as shown in FIG. 14A, since the subsequent stagesignal OUT (n+2) is not input to the last two stages of the shiftregister, a second start pulse SP2 and a third start pulse SP3 may beseparately input to the last two stages of the shift register, forexample.

Note that a clock signal (CK) is a signal which oscillates between anH-level signal and an L-level signal (also referred to as L signal or asignal at a low power supply potential level) at regular intervals.Here, the first to fourth clock signals CK1 to CK4 are delayed by ¼cycle sequentially. In this embodiment, by using the first to fourthclock signals CK1 to CK4, control or the like of driving of the pulseoutput circuits is performed. The clock signal is also referred to asGCK or SCK in accordance with a driving circuit to which the signal isinput; however, here, description is made using CK as the clock signal.

A first input terminal 21, a second input terminal 22, and a third inputterminal 23 are electrically connected to any of the first to fourthwirings 11 to 14. For example, in FIG. 14A, the first input terminal 21of the first pulse output circuit 10_1 is electrically connected to thefirst wiring 11, the second input terminal 22 of the first pulse outputcircuit 10_1 is electrically connected to the second wiring 12, and thethird input terminal 23 of the first pulse output circuit 10_1 iselectrically connected to the third wiring 13. In addition, the firstinput terminal 21 of the second pulse output circuit 10_2 iselectrically connected to the second wiring 12, the second inputterminal 22 of the second pulse output circuit 102 is electricallyconnected to the third wiring 13, and the third input terminal 23 of thesecond pulse output circuit 102 is electrically connected to the fourthwiring 14.

Each of the first to N-th pulse output circuits 10_1 to 10_N includesthe first input terminal 21, the second input terminal 22, the thirdinput terminal 23, a fourth input terminal 24, a fifth input terminal25, a first output terminal 26, and a second output terminal 27 (seeFIG. 14B). In the first pulse output circuit 10_1, the first clocksignal CK1 is input to the first input terminal 21; the second clocksignal CK2 is input to the second input terminal 22; the third clocksignal CK3 is input to the third input terminal 23; the start pulse isinput to the fourth input terminal 24; the subsequent stage signal OUT(3) is input to the fifth input terminal 25; the first output signal OUT(1) (SR) is output from the first output terminal 26; and the secondoutput signal OUT (1) is output from the second output terminal 27.

In addition to a thin film transistor (TFT) having three terminals, thethin film transistor having four terminals, which is described in theabove embodiment, can be used for each of the first to N-th pulse outputcircuits 10_1 to 10_N. FIG. 14C shows the symbol of a thin filmtransistor 28 having four terminals, which is described in the aboveembodiment. The thin film transistor 28 in FIG. 14C corresponds to thethin film transistor having four terminals described in any ofEmbodiments 1 to 5, and the symbols are used for description below. Notethat in this specification, when a thin film transistor has two gateelectrodes with a semiconductor layer therebetween, the gate electrodebelow the semiconductor layer is referred to as a lower gate electrodeand the gate electrode above the semiconductor layer is referred to asan upper gate electrode. The thin film transistor 28 is an element thatcan perform electric control between an IN terminal and an OUT terminalwith a first control signal G1 input to the lower gate electrode and asecond control signal G2 input to the upper gate electrode.

When an oxide semiconductor is used for a semiconductor layer includinga channel formation region of a thin film transistor, threshold voltageis shifted in a negative or positive direction in some cases dependingon a manufacturing process. Thus, a thin film transistor in which anoxide semiconductor is used for a semiconductor layer including achannel formation region preferably has a structure where thresholdvoltage can be controlled. The threshold voltage of the thin filmtransistor 28 shown in FIG. 14C can be controlled to a desired value inthe following manner: a gate electrode is provided on the upper and thelower sides of the channel formation region of the thin film transistor28 with a gate insulating layer interposed therebetween, and thepotential of the gate electrode on the upper and/or lower sides iscontrolled.

Next, an example of a specific circuit structure of the pulse outputcircuits is described with reference to FIG. 14D.

The first pulse output circuit 10_1 has first to thirteenth transistors31 to 43 (see FIG. 14D). In addition to the first to fifth inputterminals 21 to 25, the first output terminal 26, and the second outputterminal 27, signals or power supply potentials are supplied to thefirst to thirteenth transistors 31 to 43 from a power supply line 51 towhich a first high power supply potential VDD is supplied, a powersupply line 52 to which a second high power supply potential VCC issupplied, and a power supply line 53 to which a low power supplypotential VSS is supplied. Here, a potential relationship of each of thepower supply lines in FIG. 14D is as follows: the first power supplypotential VDD is higher than or equal to the second power supplypotential VCC, and the second power supply potential VCC is higher thanor equal to the third power supply potential VSS. Although the first tofourth clock signals CK1 to CK4 are signals which oscillate between anH-level signal and an L-level signal at regular intervals, a potentialis VDD when the clock signal is at the H-level, and the potential is VSSwhen the clock signal is at the L-level. By setting the potential VDD ofthe power supply line 51 higher than the potential VCC of the powersupply line 52, a potential applied to the gate electrode of thetransistor can be lowered without adversely affecting the operation;thus, the shift of the threshold voltage of the transistor can bereduced and deterioration can be suppressed. Note that as shown in FIG.14D, the thin film transistor 28 having four terminals shown in FIG. 14Cis preferably used for the first transistor 31 and the sixth to ninthtransistors 36 to 39 among the first to thirteenth transistors 31 to 43.The first transistor 31 and the sixth to ninth transistors 36 to 39 arerequired to switch a potential of each node connected to one ofelectrodes which is to be a source or a drain by a control signal of thegate electrode. The first transistor 31 and the sixth to ninthtransistors 36 to 39 can further reduce malfunctions of the pulse outputcircuits by quick response (sharp rising of on current) with respect toa control signal input to the gate electrode. Therefore, when a thinfilm transistor 28 having four terminals illustrated in FIG. 14C isused, the threshold voltage can be controlled and malfunctions of thepulse output circuits can be further reduced. Note that in FIG. 14D, thefirst control signal G1 is the same control signal as the second controlsignal G2; however, the first control signal G1 and the second controlsignal G2 may be different from each other.

In FIG. 14D, a first terminal of the first transistor 31 is electricallyconnected to the power supply line 51, a second terminal of the firsttransistor 31 is electrically connected to a first terminal of the ninthtransistor 39, and gate electrodes (a lower gate electrode and an uppergate electrode) of the first transistor 31 are electrically connected tothe fourth input terminal 24. A first terminal of the second transistor32 is electrically connected to the power supply line 53, a secondterminal of the second transistor 32 is electrically connected to thefirst terminal of the ninth transistor 39, and a gate electrode of thesecond transistor 32 is electrically connected to a gate electrode ofthe fourth transistor 34. A first terminal of the third transistor 33 iselectrically connected to the first input terminal 21, and a secondterminal of the third transistor 33 is electrically connected to thefirst output terminal 26. A first terminal of the fourth transistor 34is electrically connected to the power supply line 53, and a secondterminal of the fourth transistor 34 is electrically connected to thefirst output terminal 26. A first terminal of the fifth transistor 35 iselectrically connected to the power supply line 53, a second terminal ofthe fifth transistor 35 is electrically connected to the gate electrodeof the second transistor 32 and the gate electrode of the fourthtransistor 34, and a gate electrode of the fifth transistor 35 iselectrically connected to the fourth input terminal 24. A first terminalof the sixth transistor 36 is electrically connected to the power supplyline 52, a second terminal of the sixth transistor 36 is electricallyconnected to the gate electrode of the second transistor 32 and the gateelectrode of the fourth transistor 34, and gate electrodes (a lower gateelectrode and an upper gate electrode) of the sixth transistor 36 areelectrically connected to the fifth input terminal 25. A first terminalof the seventh transistor 37 is electrically connected to the powersupply line 52, a second terminal of the seventh transistor 37 iselectrically connected to a second terminal of the eighth transistor 38,and gate electrodes (a lower gate electrode and an upper gate electrode)of the seventh transistor 37 are electrically connected to the thirdinput terminal 23. A first terminal of the eighth transistor 38 iselectrically connected to the gate electrode of the second transistor 32and the gate electrode of the fourth transistor 34, and gate electrodes(a lower gate electrode and an upper gate electrode) of the eighthtransistor 38 is electrically connected to the second input terminal 22.The first terminal of the ninth transistor 39 is electrically connectedto the second terminal of the first transistor 31 and the secondterminal of the second transistor 32, a second terminal of the ninthtransistor 39 is electrically connected to a gate electrode of the thirdtransistor 33 and a gate electrode of the tenth transistor 40, and gateelectrodes (a lower gate electrode and an upper gate electrode) of theninth transistor 39 are electrically connected to the power supply line52. A first terminal of the tenth transistor 40 is electricallyconnected to the first input terminal 21, a second terminal of the tenthtransistor 40 is electrically connected to the second output terminal27, and the gate electrode of the tenth transistor 40 is electricallyconnected to the second terminal of the ninth transistor 39. A firstterminal of the eleventh transistor 41 is electrically connected to thepower supply line 53, a second terminal of the eleventh transistor 41 iselectrically connected to the second output terminal 27, and a gateelectrode of the eleventh transistor 41 is electrically connected to thegate electrode of the second transistor 32 and the gate electrode of thefourth transistor 34. A first terminal of the twelfth transistor 42 iselectrically connected to the power supply line 53, a second terminal ofthe twelfth transistor 42 is electrically connected to the second outputterminal 27, and a gate electrode of the twelfth transistor 42 iselectrically connected to the gate electrodes (the lower gate electrodeand the upper gate electrode) of the seventh transistor 37. A firstterminal of the thirteenth transistor 43 is electrically connected tothe power supply line 53, a second terminal of the thirteenth transistor43 is electrically connected to the first output terminal 26, and a gateelectrode of the thirteenth transistor 43 is electrically connected tothe gate electrodes (the lower gate electrode and the upper gateelectrode) of the seventh transistor 37.

In FIG. 14D, a connection point of the gate electrode of the thirdtransistor 33, the gate electrode of the tenth transistor 40, and thesecond terminal of the ninth transistor 39 is referred to as a node A.In addition, a connection point of the gate electrode of the secondtransistor 32, the gate electrode of the fourth transistor 34, thesecond terminal of the fifth transistor 35, the second terminal of thesixth transistor 36, the first terminal of the eighth transistor 38, andthe gate electrode of the eleventh transistor 41 is referred to as anode B (see, FIG. 15A).

Note that the thin film transistor is an element which includes at leastthree terminals: gate, drain, and source electrodes. A channel formationregion is provided between the drain region and the source region andcurrent can flow through the drain region, the channel region, and thesource region. Here, since the source and the drain of the thin filmtransistor may change depending on the structure, the operatingcondition, and the like of the thin film transistor, it is difficult todefine which is a source or a drain. Therefore, a region functioning asa source or a drain is not called a source or a drain in some cases. Insuch a case, for example, one of the source and the drain may bereferred to as a first terminal and the other thereof may be referred toas a second terminal.

Note that in FIG. 14D and FIG. 15A, a capacitor for performing bootstrapoperation by setting the node A floating may be additionally provided.Further, a capacitor having one electrode electrically connected to thenode B may be additionally provided in order to hold a potential of thenode B.

Here, FIG. 15B shows a timing chart of a shift register including aplurality of the pulse output circuits shown in FIG. 15A. Note that inthe case where the shift register is a scan line driving circuit, aperiod 61 of FIG. 15B corresponds to a vertical retrace period and aperiod 62 of FIG. 15B corresponds to a gate selection period.

Note that as shown in FIG. 15A, with the ninth transistor 39 whose gateis supplied with the second power supply potential VCC, advantagesdescribed below are obtained before and after bootstrap operation.

Without the ninth transistor 39 whose gate is supplied with the secondpower supply potential VCC, when a potential of the node A is raised bybootstrap operation, a potential of a source which is the secondterminal of the first thin film transistor 31 increases to a valuehigher than the first power supply potential VDD. Then, the firstterminal of the first transistor 31, that is, the terminal on the powersupply line 51 side, comes to serve as a source of the first transistor31. Therefore, in the first transistor 31, a high bias voltage isapplied and thus significant stress is applied between the gate and thesource and between the gate and the drain, which might causedeterioration in the transistor. Thus, with the ninth transistor 39whose gate electrode is supplied with the second power supply potentialVCC, the potential of the node A is raised by bootstrap operation, butat the same time, an increase in the potential of the second terminal ofthe first transistor 31 can be prevented. In other words, with the ninthtransistor 39, the level of a negative bias voltage applied between thegate and the source of the first transistor 31 can be lowered.Accordingly, with a circuit structure in this embodiment, a negativebias voltage applied between the gate and the source of the firsttransistor 31 can be lowered, so that deterioration in the firsttransistor 31, which is due to stress, can be further restrained.

Note that the ninth transistor 39 is provided so that the first terminaland the second terminal of the ninth transistor 39 are connected betweenthe second terminal of the first transistor 31 and the gate of the thirdtransistor 33. In the case where a shift register includes a pluralityof pulse output circuits of this embodiment, the ninth transistor 39 maybe eliminated in a signal line driving circuit which has more stagesthan a scan line driving circuit, which is advantageous in reducing thenumber of the transistors.

When an oxide semiconductor is used for each of the semiconductor layersof the first to thirteenth transistors 31 to 43, the amount of offcurrent of the thin film transistors can be reduced, the amount of oncurrent and field-effect mobility can be increased, and the rate ofdeterioration can be decreased, whereby malfunctions of the circuit canbe reduced. Further, a transistor including an oxide semiconductor has alower rate of deterioration of the transistor due to application of ahigh potential to a gate electrode, as compared to a transistorincluding amorphous silicon. Therefore, even when the first power supplypotential VDD is supplied to the power supply line to which the secondpower supply potential VCC is supplied, similar operation can beperformed and the number of power supply lines provided between thecircuits can be reduced, whereby size reduction in a circuit can beachieved.

Note that a similar effect is obtained even when a connection relationis changed so that a clock signal which is supplied to the gateelectrodes (the lower gate electrode and the upper gate electrode) ofthe seventh transistor 37 through the third input terminal 23 is a clocksignal which is supplied to the gate electrodes (the lower gateelectrode and the upper electrode) of the seventh transistor 37 throughthe second input terminal 22; and a clock signal which is supplied tothe gate electrodes (the lower gate electrode and the upper gateelectrode) of the eighth transistor 38 through the second input terminal22 is a clock signal which is supplied to the gate electrodes (the lowerelectrode and the upper electrode) of the eighth transistor 38 throughthe third input terminal 23. Note that in the shift register shown inFIG. 15A, the seventh transistor 37 and the eighth transistor 38 areboth in an on state, the seventh transistor 37 is turned off and theeighth transistor 38 is kept on, and then the seventh transistor 37 keptoff and the eighth transistor 38 is turned off, whereby the decrease inthe potential of the node B, which is caused by the decrease in thepotentials of the second input terminal 22 and the third input terminal23, occurs twice due to the decrease in the potential of the gateelectrode of the seventh transistor 37 and the decrease in the potentialof the gate electrode of the eighth transistor 38. On the other hand, inthe shift register shown in FIG. 15A, the seventh transistor 37 and theeighth transistor 38 are both in an on state, the seventh transistor 37is kept on and the eighth transistor 38 is turned off, and then theseventh transistor 37 is turned off and the eighth transistor 38 is keptoff, whereby the decrease in the potential of the node B, which iscaused by the decrease in the potentials of the second input terminal 22and the third input terminal 23, can be reduced to once due to thedecrease in the potential of the gate electrode of the eighth transistor38. Accordingly, the connection relation, in which the clock signal CK3is supplied to the gate electrodes (the lower electrode and the upperelectrode) of the seventh transistor 37 through the third input terminal23 and the clock signal CK2 is supplied to the gate electrodes (thelower gate electrode and the upper gate electrode) of the eighthtransistor 38 through the second input terminal 22, is preferable. Thatis because the number of times of fluctuation of the potential of thenode B can be reduced and noise can be reduced.

In this manner, in a period during which the potential of the firstoutput terminal 26 and the potential of the second output terminal 27are held at the L level, an H level signal is regularly supplied to thenode B; therefore, a malfunction of the pulse output circuit can beprevented.

Embodiment 11

A light-emitting device disclosed in this specification can be appliedto a variety of electronic devices (including an amusement machine).Examples of electronic devices are a television device (also referred toas a television or a television receiver), a monitor of a computer orthe like, a camera such as a digital camera or a digital video camera, adigital photo frame, a mobile phone handset (also referred to as amobile phone or a mobile phone device), a portable game console, aportable information terminal, an audio reproducing device, a largesized game machine such as a pachinko machine, and the like.

In this embodiment, an example of a mobile phone using the flexiblelight-emitting device formed according to any of the above embodimentsis shown in FIGS. 23A to 23D and FIG. 24.

FIG. 23C is a front view of a mobile phone; FIG. 23D, a side view; andFIG. 23B, a top view. Housings of the mobile phone are a housing 1411 aand a housing 1411 b. A light-transmitting supporting member is used forat least of the housing 1411 a and the housing 1411 b which is to be adisplay region. FIG. 23A is a cross-sectional view of the inside of thehousing 1411 a and the housing 1411 b. The front of the housing 1411 ahas a rectangular shape with a longer side and a shorter side, which mayhave a round corner. In this embodiment, a direction parallel to thelonger side of the rectangle that is the shape of the front is referredto as a longitudinal direction and a direction parallel to the shorterside is referred to as a lateral direction.

In addition, the sides of the housing 1411 a and the housing 1411 b alsohave a rectangular shape with a longer side and a shorter side, whichmay have a round corner. In this embodiment, a direction parallel to thelonger sides of the rectangle that is the shape of the side is alongitudinal direction, and a direction parallel to the shorter sides isreferred to as a depth direction.

The mobile phone shown in FIGS. 23A to 23D includes a display region1413, operating buttons 1404, and a touch panel 1423, and the housings1411 a and 1411 b include a light-emitting panel 1421 and a wiring board1425. The touch panel 1423 may be provided as needed.

As the light-emitting panel 1421, the light-emitting device (thelight-emitting panel or the light-emitting module) described above inEmbodiments 1 to 10 may be used.

As shown in FIGS. 23B and 23C, the light-emitting panel 1421 is arrangedalong the shape of the housing 1411 a so as to cover not only the frontregion on the viewer side but also part of the top region and the bottomregion. Therefore, a display region 1427 can be formed on the top of themobile phone in the longitudinal direction to be connected to thedisplay region 1413. That is, the display region 1427 also exists on thetop surface of the mobile phone. Accordingly, the display region 1427can be seen without taking out the mobile phone from, for example, evenif in the breast pocket.

On the display regions 1413 and 1427, incoming mails or calls, dates,phone numbers, personal names, and the like may be displayed. Further,energy consumption can be saved by performing display only in thedisplay region 1427 and not performing display in the other regions asneeded.

FIG. 24 shows the cross-sectional view of FIG. 23D. As shown in FIG. 24,the light-emitting panel 1421 is continuously formed on the top, front,and bottom of the inside of the housing 1411 a. A battery 1426 and thewiring board 1425 electrically connected to the light-emitting panel1421 are arranged in the backside of the light-emitting panel 1421. Inaddition, the touch panel 1423 is arranged in the outside of the housing1411 a (on the viewer side).

Images and letters can be displayed, whether the mobile phone of thisembodiment is placed horizontally or vertically.

The light-emitting panel 1421 is not manufactured separately in thefront region and the top region, but manufactured to cover both thefront display region 1413 and the top display region 1427, wherebymanufacturing cost and time can be reduced.

The touch panel 1423 is arranged on the housing 1411 a, and buttons 1414of the touch panel are displayed on the display region 1413. By touchingthe buttons 1414 with a finger or the like, contents displayed on thedisplay region 1413 can be operated. Further, making calls or composingmails can also be performed by touching the buttons 1414 on the displayregion 1413 with a finger or the like.

The buttons 1414 on the touch panel 1423 may be displayed when needed,and when the buttons 1414 are unneeded, images or letters can bedisplayed on the entire display region 1413.

Furthermore, the upper longer side in a cross section of the mobilephone may also have a radius of curvature. When the mobile phone isformed so that the cross section thereof has a radius of curvature inthe upper longer side, the light-emitting panel 1421 and the touch panel1423 also have a radius of curvature in an upper longer side in a crosssection. In addition, the housing 1411 a also has a curved shape. Inother words, the display region 1413 on the front is curved outwards.

FIGS. 25A and 25B show an example of an electronic book reader using theflexible light-emitting device formed according to any of the aboveembodiments. FIG. 25A shows an opened electronic book reader and FIG.25B shows a closed electronic book reader. The light-emitting device(the light-emitting panel) formed according to any of the aboveembodiments can be used for a first display panel 4311, a second displaypanel 4312, and a third display panel 4313.

A first housing 4305 has the first display panel 4311 including a firstdisplay portion 4301, a second housing 4306 has the second display panel4312 including an operation portion 4304 and a second display portion4307. The third display panel 4313 is a dual display type panel and hasa third display portion 4302 and a fourth display portion 4310. Thethird display panel 4313 is interposed between the first display panel4311 and the second display panel 4312. The first housing 4305, thefirst display panel 4311, the third display panel 4313, the seconddisplay panel 4312, and the second housing 4306 are connected to eachother with a binding portion 4308 in which a driving portion is formed.The electronic book reader of FIGS. 25A and 25B includes four displayscreens of the first display portion 4301, the second display portion4307, the third display portion 4302, and the fourth display portion4310.

The first housing 4305, the first display panel 4311, the third displaypanel 4313, the second display panel 4312, and the second housing 4306are each flexible and has high flexibility. Further, when a plasticsubstrate is used for each of the first housing 4305 and the secondhousing 4306, and a thin film is used for the third display panel 4313,a thin electronic book reader can be obtained.

The third display panel 4313 is a dual display type panel including thethird display portion 4302 and the fourth display portion 4310. For thethird display panel 4313, a display panel of a dual emission type may beused, or display panels of a one-side emission type may be bonded.

FIG. 26 is an example in which the light-emitting device formedaccording to any of the above embodiments is used as an indoor lightingdevice 3001. Since the light-emitting device shown in the aboveembodiments can be increased in area, the light-emitting device can beused as a lighting device having a large area. Further, thelight-emitting device shown in the above embodiments can be used as adesk lamp 3000. Note that the lighting equipment includes in itscategory, a ceiling light, a desk light, a wall light, a lighting for aninside of a car, an emergency exit light, and the like.

As described above, the light-emitting device shown in Embodiments 1 to10 can be arranged in the display panels of the above various electronicdevices; thus, an electronic device with high reliability can beprovided.

This application is based on Japanese Patent Application serial no.2009-215053 filed with Japan Patent Office on Sep. 16, 2009, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: a flexiblesubstrate; a driving circuit portion over the flexible substrate,comprising: a first transistor comprising: a first gate over theflexible substrate; an insulating layer over the first gate; a firstoxide semiconductor layer over the insulating layer; a first source overthe first oxide semiconductor layer; a first drain over the first oxidesemiconductor layer; an oxide insulating layer over the first oxidesemiconductor layer, the first source, and the first drain, a part ofthe oxide insulating layer being in contact with a part of the firstoxide semiconductor layer between the first source and the first drain;and a conductive layer over the oxide insulating layer, the conductivelayer overlapping with the first gate and a channel region of the firsttransistor, wherein the channel region is between the first source andthe first drain; a pixel portion over the flexible substrate,comprising: a second transistor comprising: a second gate over theflexible substrate; the insulating layer over the second gate; a secondoxide semiconductor layer over the insulating layer; a second sourceover the second oxide semiconductor layer; a second drain over thesecond oxide semiconductor layer; and the oxide insulating layer overthe second oxide semiconductor layer, the second source, and the seconddrain, a part of the oxide insulating layer being in contact with a partof the second oxide semiconductor layer between the second source andthe second drain; a color filter over the oxide insulating layer; afirst electrode layer over the color filter and electrically connectedto the second transistor; an EL layer over the first electrode layer;and a second electrode layer over the EL layer; and a terminal portioncomprising: a third electrode layer over the flexible substrate; theinsulating layer over the third electrode layer, the insulating layerincluding a first contact hole; a fourth electrode layer over and incontact with the third electrode layer through the first contact hole;the oxide insulating layer over the fourth electrode layer, the oxideinsulating layer including a second contact hole; and a fifth electrodelayer over and in contact with the fourth electrode layer through thesecond contact hole, wherein the third electrode layer is formed from asame layer as the first gate, wherein the fourth electrode layer isformed from a same layer as the first source and the first drain,wherein the fifth electrode layer is formed from a same layer as theconductive layer, and wherein the driving circuit portion is locatedoutside the pixel portion.
 2. The semiconductor device according toclaim 1, wherein the conductive layer is a light-transmitting conductivefilm formed in the same process as the first electrode layer.
 3. Thesemiconductor device according to claim 1 further comprising: a firstoxide conductive layer provided between the first oxide semiconductorlayer and the first source; a second oxide conductive layer providedbetween the first oxide semiconductor layer and the first drain; a thirdoxide conductive layer provided between the second oxide semiconductorlayer and the second source; and a fourth oxide conductive layerprovided between the second oxide semiconductor layer and the seconddrain.
 4. The semiconductor device according to claim 1, furthercomprising a flexible metal substrate over the first transistor and thesecond transistor, wherein the driving circuit portion and the pixelportion are sealed with the flexible metal substrate.
 5. Thesemiconductor device according to claim 1, further comprising apartition covering a periphery of the first electrode layer, wherein thepartition does not overlap with the first transistor.
 6. Thesemiconductor device according to claim 1, wherein the color filter doesnot overlap with either the first oxide semiconductor layer or thesecond oxide semiconductor layer.
 7. A semiconductor device comprising:a flexible substrate; a driving circuit portion over the flexiblesubstrate, comprising: a first transistor comprising: a first gate overthe flexible substrate; an insulating layer over the first gate; a firstoxide semiconductor layer over the insulating layer; a first source overthe first oxide semiconductor layer; a first drain over the first oxidesemiconductor layer; an oxide insulating layer over the first oxidesemiconductor layer, the first source, and the first drain, a part ofthe oxide insulating layer being in contact with a part of the firstoxide semiconductor layer between the first source and the first drain;and a conductive layer over the oxide insulating layer, the conductivelayer overlapping with the first gate and a channel region of the firsttransistor, wherein the channel region is between the first source andthe first drain; a pixel portion over the flexible substrate,comprising: a color filter over the oxide insulating layer; a firstelectrode layer over the color filter; an EL layer over the firstelectrode layer; and a second electrode layer over the EL layer; and aterminal portion comprising: a third electrode layer over the flexiblesubstrate; the insulating layer over the third electrode layer, theinsulating layer including a first contact hole; a fourth electrodelayer over and in contact with the third electrode layer through thefirst contact hole; the oxide insulating layer over the fourth electrodelayer, the oxide insulating layer including a second contact hole; and afifth electrode layer over and in contact with the fourth electrodelayer through the second contact hole, wherein the third electrode layeris formed from a same layer as the first gate, wherein the fourthelectrode layer is formed from a same layer as the first source and thefirst drain, and wherein the fifth electrode layer is formed from a samelayer as the conductive layer.